Author Topic: Fy6800 vs Fy6900  (Read 16500 times)

0 Members and 2 Guests are viewing this topic.

Offline Adrian_Arg.

  • Regular Contributor
  • *
  • Posts: 249
  • Country: ar
Fy6800 vs Fy6900
« on: July 01, 2019, 10:16:57 pm »
Hi, I was able to get a question this is the same FY6800, with different shell and other numeracion. functionally they must be the same. [url] https://es.aliexpress.com/item/33034872134.html [/ url] |O
 

Offline windsmurf

  • Frequent Contributor
  • **
  • !
  • Posts: 643
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #1 on: July 02, 2019, 02:15:08 am »
It looks like they upgraded the FY6800... specs look different, esp. 0-24Vpp...
- MagicPulse Technology,Low Jitter(RMS)<200ps
- Various Modulation: AM,FM,PM,ASK,FSK,PSK
- More Than 100 Waveforms: 8192 points * 14bits
- 0~24Vpp Amplitude Range,Min Resolution 1mV
 

Offline CDaniel

  • Frequent Contributor
  • **
  • Posts: 316
  • Country: ro
Re: Fy6800 vs Fy6900
« Reply #2 on: July 02, 2019, 04:41:20 pm »
If you got the old version is not worth it , maybe if the jitter for square wave is indeed much smaller .
That stupid display mode with many leading zeros is the same ...
« Last Edit: July 02, 2019, 04:43:00 pm by CDaniel »
 

Offline Andbro

  • Regular Contributor
  • *
  • Posts: 99
Re: Fy6800 vs Fy6900
« Reply #3 on: July 02, 2019, 07:41:24 pm »
Hi,

What is the difference between the FY6900 sold by Kkmoon and the other sold by Feelelec? Who is Kkmoon?

Thanks
 

Offline windsmurf

  • Frequent Contributor
  • **
  • !
  • Posts: 643
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #4 on: July 03, 2019, 12:37:47 am »
KKMoon just appears to be a reseller that rebrands other company's equipment.
FeelElec I think is the original manufacturer, also known as FeelTech.

 

Offline Adrian_Arg.

  • Regular Contributor
  • *
  • Posts: 249
  • Country: ar
Re: Fy6800 vs Fy6900
« Reply #5 on: July 03, 2019, 01:33:22 am »
I had a fy6600, this one died, but for $ 100 I wanted to try the fy6900, I know that for that money you can not demand much.
 :-//
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #6 on: July 03, 2019, 03:01:46 am »
It looks like they upgraded the FY6800... specs look different, esp. 0-24Vpp...
- MagicPulse Technology,Low Jitter(RMS)<200ps
- Various Modulation: AM,FM,PM,ASK,FSK,PSK
- More Than 100 Waveforms: 8192 points * 14bits
- 0~24Vpp Amplitude Range,Min Resolution 1mV

 I'm afraid it's the other way round. It's actually a DOWNGRADE not only on the 6800 but also on the 6600 models >:(

 See my reply in the original FY6600 thread after I'd read through the manual for the FY6900

https://www.eevblog.com/forum/testgear/feeltech-fy6600-60mhz-2-ch-vco-function-arbitrary-waveform-signal-generator/msg2475843/#msg2475843

 I have a tendency to marathon postings but fear not, the above linked posting tells you all you need to know to save your pennies for better things (like an FY6600-60M for just 40 quid from Hong Kong!  ;) ).

 Seriously, you'd be better off imho, getting hold of the 6800 instead of the 6900 (but that 40 quid 6600 is such a bargain and the specification so identical to the 6800 it's hard to resist).  At that price, I couldn't resist buying myself a 'spare' but the one I ordered just on four weeks ago now is supposed to be arriving no later than today. I'll believe that when I see it. Fortunately, I'm not in any great hurry.

JBG

PS I only noticed this " MagicPulse Technology,Low Jitter(RMS)<200ps" you'd included in the feature list after posting my reply. It rather looks like you've conflated the specs of another make of DDS AWG since, after a long hard look at the FY6900 manual, I could find no mention of this feature at all which is rather odd considering that such a feature would put it in an entirely different league to that of its predecessors.
« Last Edit: July 03, 2019, 03:46:02 am by Johnny B Good »
 

Offline vinlove

  • Frequent Contributor
  • **
  • Posts: 329
Re: Fy6800 vs Fy6900
« Reply #7 on: July 03, 2019, 06:57:45 am »
I got a KKMoon FY6800 for 59£ recently, and it is great.

Only problem was there was no manual with it, so I have been watching Youtube reviews on it.
I still need to find out how to use 50-60% of its capabilities.
 

Offline windsmurf

  • Frequent Contributor
  • **
  • !
  • Posts: 643
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #8 on: July 03, 2019, 07:15:53 am »
It looks like they upgraded the FY6800... specs look different, esp. 0-24Vpp...
- MagicPulse Technology,Low Jitter(RMS)<200ps
- Various Modulation: AM,FM,PM,ASK,FSK,PSK
- More Than 100 Waveforms: 8192 points * 14bits
- 0~24Vpp Amplitude Range,Min Resolution 1mV

...
PS I only noticed this " MagicPulse Technology,Low Jitter(RMS)<200ps" you'd included in the feature list after posting my reply. It rather looks like you've conflated the specs of another make of DDS AWG since, after a long hard look at the FY6900 manual, I could find no mention of this feature at all which is rather odd considering that such a feature would put it in an entirely different league to that of its predecessors.

I don't recall where I got that, but similar info is here:
https://m.banggood.com/marketing-Multimeter-Signal-Generator--Oscilloscope-Promotion/tid-1801.html

 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #9 on: July 03, 2019, 09:12:12 am »
It looks like they upgraded the FY6800... specs look different, esp. 0-24Vpp...
- MagicPulse Technology,Low Jitter(RMS)<200ps
- Various Modulation: AM,FM,PM,ASK,FSK,PSK
- More Than 100 Waveforms: 8192 points * 14bits
- 0~24Vpp Amplitude Range,Min Resolution 1mV

...
PS I only noticed this " MagicPulse Technology,Low Jitter(RMS)<200ps" you'd included in the feature list after posting my reply. It rather looks like you've conflated the specs of another make of DDS AWG since, after a long hard look at the FY6900 manual, I could find no mention of this feature at all which is rather odd considering that such a feature would put it in an entirely different league to that of its predecessors.

I don't recall where I got that, but similar info is here:
https://m.banggood.com/marketing-Multimeter-Signal-Generator--Oscilloscope-Promotion/tid-1801.html

 Thank you for that swift response. So, not your fault for that errata.  ;)  It's all down to Bangood playing fast and loose with the facts as usual. >:(

 Having solved that little mystery, there's nothing to change my opinion of Feeltech's latest version of the FY6600/6800 then.

[EDIT]   Out of curiosity, I checked out both manuals (V2.2 and 2.9) for the FY6600 and the one manual I have for the FY6800 and was surprised to see the same claim on output levels of 20Vpp max in the zero to 10MHz range with a 10Vpp max over the 10>20MHz range and a 5Vpp limit thereafter. This is contrary to the reality (at least as far as the sine wave option goes - I didn't bother checking the other wave forms) where no such 10Vpp limit exists. What you get with the sine wave option is a max of 20Vpp from 0Hz to 20MHz beyond which it drops straight down to 5Vpp (no 10Vpp limit for sine waves at least).

 Those limits, ISTR,  only apply to non-sinusoidal waveforms so it looks like an omission in all the user manuals regarding the extended 20Vpp frequency limit for sine wave output. I suspect the 6900 might follow the same pattern but the manual is no guide in this matter. As soon as anyone gets hold of a sample, this should be the first thing to check and report on since it would mean it's not quite the downgrade implied by the output figures published in the 6900's manual after all.

JBG
« Last Edit: July 03, 2019, 03:02:49 pm by Johnny B Good »
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #10 on: July 03, 2019, 11:28:16 am »
I got a KKMoon FY6800 for 59£ recently, and it is great.

Only problem was there was no manual with it, so I have been watching Youtube reviews on it.
I still need to find out how to use 50-60% of its capabilities.

 You can download the manual from here

http://en.feeltech.net/index.php?case=archive&act=list&catid=6

JBG
 

Offline Adrian_Arg.

  • Regular Contributor
  • *
  • Posts: 249
  • Country: ar
Re: Fy6800 vs Fy6900
« Reply #11 on: July 03, 2019, 04:11:05 pm »
ok, then I'm going to go for a fy6800
 

Offline GreyWoolfe

  • Super Contributor
  • ***
  • Posts: 3365
  • Country: us
  • NW0LF
Re: Fy6800 vs Fy6900
« Reply #12 on: July 03, 2019, 04:56:11 pm »
I got a KKMoon FY6800 for 59£ recently, and it is great.

Only problem was there was no manual with it, so I have been watching Youtube reviews on it.
I still need to find out how to use 50-60% of its capabilities.

 You can download the manual from here

http://en.feeltech.net/index.php?case=archive&act=list&catid=6

JBG

Even though the folder says manual, it is actually the PC software.
"Heaven has been described as the place that once you get there all the dogs you ever loved run up to greet you."
 

Offline Adrian_Arg.

  • Regular Contributor
  • *
  • Posts: 249
  • Country: ar
 

Offline Electro Fan

  • Super Contributor
  • ***
  • Posts: 1956
Re: Fy6800 vs Fy6900
« Reply #14 on: July 03, 2019, 06:22:57 pm »
I've read about a zillion pages on the FY6XXX.  Still not clear on the connectors on the back.  Any chance one of those connectors will accept a 10 MHz reference input signal?
 

Offline GreyWoolfe

  • Super Contributor
  • ***
  • Posts: 3365
  • Country: us
  • NW0LF
"Heaven has been described as the place that once you get there all the dogs you ever loved run up to greet you."
 

Offline tinhead

  • Super Contributor
  • ***
  • Posts: 1914
  • Country: 00
    • If you like my hacks, send me a donation
Re: Fy6800 vs Fy6900
« Reply #16 on: July 03, 2019, 09:06:59 pm »
https://m.banggood.com/marketing-Multimeter-Signal-Generator--Oscilloscope-Promotion/tid-1801.html

fuck yeah! Just read this -> "Can choose our FYA2000S series or FPA1000 series power amplifier to output 20W~100W signal in DC-10MHz width without any distortion"

100W, 10MHz without ANY distortion, with an power app with 10kHz bandwidth, they made my day ...
I don't want to be human! I want to see gamma rays, I want to hear X-rays, and I want to smell dark matter ...
I want to reach out with something other than these prehensile paws and feel the solar wind of a supernova flowing over me.
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #17 on: July 03, 2019, 11:49:23 pm »
I've read about a zillion pages on the FY6XXX.  Still not clear on the connectors on the back.  Any chance one of those connectors will accept a 10 MHz reference input signal?

 No chance of that. They're all accounted for in the manual. However, don't let that stop you fitting another socket (BNC or an SMA-F) and following in Arthur Dent's footsteps, linked to below (or mine when I finally get round to adding an SMA-F socket to complement my version of Arthur's OCXO upgrade).  :)


https://www.eevblog.com/forum/testgear/feeltech-fy6600-60mhz-2-ch-vco-function-arbitrary-waveform-signal-generator/msg1346454/#msg1346454

 Since I chose to modify the existing PSU board (https://www.eevblog.com/forum/testgear/feeltech-fy6600-60mhz-2-ch-vco-function-arbitrary-waveform-signal-generator/msg2310768/#msg2310768) rather than replace it, I had to add the innards of a small 12v 300mA smpsu wallwart to power my own OCXO upgrade. This gave me the advantage over Arthur's setup in that I could wire this directly to the C6 mains socket I'd fitted to overcome the ESD risk posed to any DUT so I could turn the generator off on the rear panel switch and keep the OCXO running whilst the unit remained plugged into a live mains outlet.

 Using the the front panel "Standby" button only turns the display off by way of a power saving of circa 1 or 2 watts at most, leaving it to consume some 5 watts or so. The consumption of the OCXO once up to temperature is a mere 1.35W from the mains (the OCXO itself only consumes some 700mW naked or around 600mW when blanketed with quarter inch thick rubber foam - primarily to buffer it against random wind chill effects from the cooling fan).

 I'm planning on avoiding the issues of using a switch to select between the internal and external frequency references by using the "Injection Locking" technique whereby the external reference is used to couple remarkably little, yet more than ample, energy into the local OCXO to cause it to lock to the external reference automatically without the need for a change over switch.

  I've already proved that the 10MHz CQE OCXOs I'm using can be locked over a +/-10ppb range quite readily via their output pins which, since an error of as much as 1ppb can now be regarded as outrageously off frequency, is a more than ample lock in range (I've been able to trim to within 50ppt of my basic fledgling GPSDO[1] and see the OCXO in my FY6600 stay within +/- 70ppt for a week or more making long term calibration to within 0.5ppb a realistic goal).

[1] I've been experimenting with GPS modules for several months now and only recently acquired a collection of OCXOs to develop the original raw 10MHz PPS output calibration standard into a proper, if rather basic[2], GPSDO. Currently I have it assembled onto a prototyping board which I've been tinkering with for more weeks than was strictly necessary.

 I finally shut it, the 'scope and the FY6600 down just a few days ago to get used to the idea of not being able to glance at the 'scope trace evidence of my successes with the FY6600 OCXO mod and the GPSDO project by well of self admiration at getting so close to boxing off my first homebrewed GPSDO project. It seems I'm finally ready to take that boxing off step since, surprisingly, I didn't feel any obvious symptoms of "Going Cold Turkey".  8)

 I guess the knowledge that the only way forward now to get away from the susceptibility to "Theremin Effect" induced phase shifts and other prototyping board layout induced instabilities, is to actually commit it all to a PCB fitted into a nice metal enclosure to shield it from external environmental influences.

 Once I've sorted out the GPSDO, I'll be able to turn my attention back to the task of fitting an SMA-F external reference socket and injection locking circuitry into the FY6600. I'll take a bunch of photos to make a "Show and Tell" post in the FY6600 thread when I've completed this (final???) modification. It'll probably take me a few weeks to get to this stage so don't wait for this with bated breath.

[2] Basic in the sense that I'm just using a two pole RC LPF on the phase detector output which, whilst sufficient to suppress the jitter on frequencies that are derived using non-integer divide ratios of the 48MHz clock and deal with the sawtooth adjustments, does not have the long term averaging effect of a micro-controller filtering algorithm to filter out the basic GPS navigation system shortcomings in handling ionospheric variations which reflect as nanoseconds worth of phase shift (typically as much as +/-15ns over periods of 30 to 300 seconds and beyond) on the PPS signal (100KHz setting in the U-blox M8N (fake) module I'm currently using to phase lock my 10MHz OCXO to).

 Whilst these phase variations don't fatally detract from the process of confirming that a free running OCXO or Rubidium clock is already within a few PPT of nominal, trying to make recalibration adjustments otoh, becomes rather a matter of 'dumb luck'  and persistence when it comes to any attempt at trimming an OCXO to within 50ppt of frequency. :(

JBG
« Last Edit: July 06, 2019, 08:07:11 pm by Johnny B Good »
 
The following users thanked this post: Rx7man, windsmurf

Offline Rx7man

  • Contributor
  • Posts: 26
  • Country: ca
  • Hobbyist/Hack/Farmer
Re: Fy6800 vs Fy6900
« Reply #18 on: July 06, 2019, 08:16:02 pm »
If you got the old version is not worth it , maybe if the jitter for square wave is indeed much smaller .
That stupid display mode with many leading zeros is the same ...
I wish they'd change it so rather than displaying kHz when under 1khz it would just display Hz, likewise for Mhz when in that range
 

Offline Adrian_Arg.

  • Regular Contributor
  • *
  • Posts: 249
  • Country: ar
Re: Fy6800 vs Fy6900
« Reply #19 on: July 09, 2019, 06:55:18 pm »
One more question, Feeltech, Feelec and KKmoon are all the same instruments, just change the name? :popcorn:
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #20 on: July 10, 2019, 04:22:53 am »
- MagicPulse Technology,Low Jitter(RMS)<200ps

not so much in comparison with 2 ns jitter in the previous version.
Do they planning update with jitter improvement for older models?
 

Offline pantelei4

  • Regular Contributor
  • *
  • Posts: 90
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #21 on: July 10, 2019, 04:09:13 pm »
not so much in comparison with 2 ns jitter in the previous version.
Hi. In the previous version, one clock jitter 4ns.
« Last Edit: July 10, 2019, 04:10:47 pm by pantelei4 »
 

Offline MM0SDK

  • Newbie
  • Posts: 2
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #22 on: July 11, 2019, 01:34:44 am »
Hi folks, my first post here. Has anyone got their hands on the latest model yet for test? Was going to order a FY6600 or FY6800, but if there are going to be any improvements with the 6900 aside from a different enclosure, I may wait.
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #23 on: July 11, 2019, 02:46:25 am »
Hi. In the previous version, one clock jitter 4ns.

OMG. By the way, this is peak jitter, so in average, RMS jitter will be a little smaller  ;D
« Last Edit: July 11, 2019, 02:48:04 am by radiolistener »
 

Offline bdunham7

  • Frequent Contributor
  • **
  • Posts: 330
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #24 on: July 11, 2019, 09:35:16 pm »
 If it hasn't already been said, the 4ns "jitter" is just the natural result of a 250 MSa/s fixed clock DDS putting out a square wave with a period that is not a multiple of 4ns.  Sine waves don't have this jitter, so if you need a clock, try a sine wave. 

Does anyone actually have an FY6900 in hand yet? I seriously doubt they've added variable clock or "Magic Pulse" as that would be a major revision and upgrade.
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #25 on: July 12, 2019, 02:42:58 am »
If it hasn't already been said, the 4ns "jitter" is just the natural result of a 250 MSa/s fixed clock DDS putting out a square wave with a period that is not a multiple of 4ns.  Sine waves don't have this jitter, so if you need a clock, try a sine wave. 

Does anyone actually have an FY6900 in hand yet? I seriously doubt they've added variable clock or "Magic Pulse" as that would be a major revision and upgrade.

 Since no such feature gets a mention in the manual, I'd say your doubts are well founded.  :)

 Mind you, when it comes to the output level versus frequency limits specified in all the manuals for the 6600 and 6800 models, they can't be relied on as accurate sources of such information. As far as sine and square waves go, there's no such 10Vpp limit in the 10 to 20MHz range for either of those models despite what was written in their manuals. The 20Vpp limit runs all the way from DC to 20MHz before dropping straight down to a 5Vpp limit from there onward.

 The FY6900 may well do the same, contrary to what is claimed in its manual. If this does prove to be the case, then it may indeed be worthy of consideration provided it isn't burdened with a hefty price premium. Although the 24Vpp spec for DC to 5MHz is more a novelty feature, that and the increase from a +/-10v dc offset to a +/-12v dc offset does strongly imply some sort of PSU upgrade from a (nominal) +/-12v opamp rail supply to a +/-15v rail supply.

 Whilst owners of the earlier models (FY6600 and 6800) will see little to no point in purchasing an FY6900 as an 'upgrade', for anyone else contemplating a cheap two channel function generator as an initial purchase for their hobby workbench, the FY6900 would be an obvious choice over its predecessors, assuming it has the same Vpp limits as its predecessors (aside from the 0 to 5MHz 24Vpp upgrade) and is only marginally more pricey.

 I notice that they've added a cooling fan to this model. Not so much a 'luxury item' as an essential component that should have been part of the earlier models' features from the start. With the FY6800's mains inlet socket upgrade from the cheap and nasty C8 connector that had afflicted the FY6600 to a C14 connector giving access to a protective earth pin for use as a high resistance "Static Drain" connection to eliminate the half live mains leakage without introducing ground loop issues, that takes care of two of the many modifications that had to be applied to the FY6600,

 Although the ground loop issue Feeltech introduced by strapping the BNC shield connections directly to the protective earth still needs a simple resistor mod to correct this mistake, at least the hard work of the original modification needed in the case of the FY6600 has already been done, reducing it to a simple matter of adding a 1 to 10 k resistor to eliminate the ground loop issue and still keep the benefit of half mains live voltage leakage suppression (a 10KR is enough to drop the half mains live leakage potential of circa 110v on a 230v supply to just half a volt).

 If they've finally taken this opportunity to fix their 86 ohm attenuator pad 'skoolboy howler' by updating the BOM to replace just six smd resistors to correct it to a 50 ohm attenuator, this could well be the icing on the cake that might persuade some FY6600 owners (especially those with a 15, 20 or 30 MHz specced model) to "upgrade". However, if Feeltech stay true to form, this remains an unlikely prospect.

 With all of those observations in mind, I can't wait to see what a competently executed review and tear down youtube video will reveal when it is finally released to the market.  >:D

[EDIT] After posting this missive, I decided to have a quick look for any FY6900 video reviews on youtube but, as previously, it was blissfully unaware such a device even existed. However, I did come across this interesting reminder as to why these Feeltech offerings are such stonking good value ;)



 The Siglent SDG1032X Signal Generator is £360 from their UK agent with the SDG1062X another £80 to get the version that most closely resembles the 60MHz sine wave frequency spec of the FY6600-60M and the FY6800-60M models.

 You can compare the specs between the 32 and 62 models here:-

http://www.labtronix.co.uk/drupal/sites/default/files/sdg1000x/SDG1000X_DataSheet_DS0201X_E01A.pdf

 As for the Rigol DS1022 in that shoot out video, that sucks even more the the Siglent did which fell short in so many ways against the trusty Feeltech products we've all come to know and love/hate. ;)

 That shoot out video was such an eye opener as to just how good a bargain these Feeltech signal/function generators actually are, I thought I'd provide a link to it as a reminder to those who nitpick criticise the FY66/68, forgetting completely that even brand named kit with prices that start at a minimum of five times higher have their own shortcomings and limitations which make the Feeltech kit superior in some aspects of their specifications (eg the inability to produce square wave outputs at 20Vpp beyond 5 and 10 MHz for the Rigol and Siglent respectively versus the FY6600 and 6800's 20MHz limits). Mind you, I wasn't impressed by the reviewer's use of a 70MHz BW 'scope and an unterminated BNC cable in his test setup.

 The next time you want to nitpick over the irritating use of mcroHertz and milliHertz units in the frequency display (having forgotten that you can cycle through the units on the 6600's rotary encoder's push button function or the 6800's "OK" button), just remind yourself that you've saved yourself at least 280 quid on a "Decent Signal Generator". ;) If that pleasant thought fails to provide consolation, then you have to ask yourself "Why the f*ck did I waste my money on a "cheap 'n' cheerful" Feeltech generator in the first place?".

 Let's face it, the most intractable issue with the FY series of signal generators is their 4ns jitter on pulse and square waves which, quite frankly, are more a cosmetic issue in 'scope traces rather than of any real consequence to a properly designed digital process which should cheerfully take such modest amounts of jitter in its stride.

 For Christ's sake, the PC motherboard manufacturers have been offering a 'jitter' function on the clock signals for over a decade now under the label of "Spread Spectrum" taking full advantage of the logic circuits' inherent tolerance to jitter to minimise the impact of any RFI emissions that could otherwise interfere with other users of the radio spectrum.

 Obviously, there will be circumstances where this jitter will be a liability, demanding the spend of another 500 quid or more to run these more demanding test sequences. However, in a hobbyist context, the issue of jitter is less likely to arise. If it does, then the poor hobbyist is simply going to either have to use a cunning work around or else bite the bullet and track down a second hand 'bargain' that will serve this need.

 As a 'heads up', it seems to me that one cunning work around (to save spending 500 quid or more) would be to use the Sinc pulse output to drive a Schmitt triggered input gate or buffer of the appropriate logic family to match what you're testing since, like the sine wave output, this also seems to be free of this 4ns jitter which, unlike the sine wave, offers faster rise and fall times more suited to triggering pulses or square waves with well defined edges.

JBG
« Last Edit: July 12, 2019, 04:59:18 pm by Johnny B Good »
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #26 on: July 12, 2019, 03:51:47 pm »
Sine waves don't have this jitter, so if you need a clock, try a sine wave. 

sine wave has exactly the same jitter. But sine wave has more slow slope, and this jitter is hidden behind slow slope. Since slope is too slow, amplitude change will be very small, so you will not see it in time domain. But you will see it on frequency domain.

If it hasn't already been said, the 4ns "jitter" is just the natural result of a 250 MSa/s fixed clock DDS putting out a square wave with a period that is not a multiple of 4ns. 

Such jitter will be "natural result" for DAC with fixed sample rate. But FY6900 has FPGA and can use any desired sample rate for DAC, so this is not the case for FY6900 hardware. FY6900 can produce signal with better jitter, just by using variable sample rate. Yeah it's a little bit more complicated, but it is possible and it's worth it. So, this jitter is just a software limitation in FPGA code and can be reduced by software patch.
« Last Edit: July 12, 2019, 03:55:15 pm by radiolistener »
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #27 on: July 12, 2019, 10:35:28 pm »
Sine waves don't have this jitter, so if you need a clock, try a sine wave. 

sine wave has exactly the same jitter. But sine wave has more slow slope, and this jitter is hidden behind slow slope. Since slope is too slow, amplitude change will be very small, so you will not see it in time domain. But you will see it on frequency domain.

If it hasn't already been said, the 4ns "jitter" is just the natural result of a 250 MSa/s fixed clock DDS putting out a square wave with a period that is not a multiple of 4ns. 

Such jitter will be "natural result" for DAC with fixed sample rate. But FY6900 has FPGA and can use any desired sample rate for DAC, so this is not the case for FY6900 hardware. FY6900 can produce signal with better jitter, just by using variable sample rate. Yeah it's a little bit more complicated, but it is possible and it's worth it. So, this jitter is just a software limitation in FPGA code and can be reduced by software patch.

 Yes, you'd expect to see the same jitter effect on sine waves if you use a high enough frequency (10MHz 10Vpp setting driving into a 50R terminated cable - 5Vpp to the scope) and pick a fast timebase such as 10 or 5 ns per division but in actual fact you don't (at least not with the souped up FY6600-60M I'm using).

 I tried my best to track down a youtube video demonstrating and explaining this effect but, surprise surprise >:(, to no fekin' avail, hence my running some tests of my own (now that I've gotten bored with waiting for the Sinc pulse to drag itself into phase with the next GPSDO rising edge of its 10MHz clock output at the rate of 20 minutes per transit).

 One of the unexpected benefits of going OTT in the FY6600 reference oscillator upgrade to a 10MHz OCXO with a five times multiplier chip displacing the original and execrable ten a dime smd 50MHz XO is being able to observe the 4ns jitter on a 10MHz square wave in slow motion when you detune from 10MHz by just 8mHz.  8)

 I've got the 'scope triggering ch2 from the GPSDO with the FY6600 feeding ch1 at an 8mHz offset from the exact 10MHz which otherwise hides this jitter through sheer synchronicity with the FPGA's 50MHz clock which is also used to generate the 250MHz clock which drives the DAC.

 I've dropped the timebase right down to 200ns per division and zoomed in on the section at the RHS of the display (1.04μs delay) with an effective 10ns per division on the zoomed view, allowing me to observe jitter of any sort some ten cycles away from the trigger point to amplify any accumulated jitter.

 I'm pleased to report that I can observe no signs of accumulated jitter which is a tribute to both the signal generator and the 'scope (a Siglent SDS 1202X-E btw). However, at this 8milliHertz offset, I can see the square wave slowly shuffle along from right to left one set of rising then falling flanks at a time at a cycle rate of 200mHz (a 5 second period). When it comes to observing the behaviour of sine and (surprisingly) triangle waves, there is absolutely no evidence of this 4ns jitter, just a continuous and smooth leftwards drift.

 A quick scan through all the other preloaded waveforms reveals that some 50% or more are likewise free of this 4ns jitter, including quite obviously, my favourite for 'scope trace frequency comparison, the Sinc-Pulse waveform.

 I won't waste any more electrons describing which do and which don't suffer this 4ns jitter effect, in part because ICBA but mostly so as not to spoil the surprise for anyone else who has replaced the shitty little smd XO with at least a half decent TCXO to endow their much modded FY6600s and FY6800s with at least sufficient frequency stability (if not accuracy - using a 10MHz NPL grade frequency reference isn't actually required for this exercise) to observe which waveforms are and aren't effected.

 For those who haven't bothered with such an upgrade - good news! It seems you're in luck. I've stopped triggering from the GPSDO and I can still observe the jitter in slow motion. The difference being that the lack of sideways drift means the square wave only shows the effect on the falling edge with the rising edge staying put despite being delayed some 1.04μs from the trigger point. However, I suspect the original XO chip may allow some jitter to creep in with this much delay. If this proves the case, you can simply observe at the trigger point without any large delay (you'll only lose out on observing the peculiar crabbing effect of triggering from a 10MHz reference whilst the generator is offset by 8mHz) >:D

 Those comments about the FY6900 having a FPGA (they all do) which can be programmed to reduce jitter with a firmware patch, are rather intriguing. Do you have inside information on such a firmware update which Feeltech/Feelec have seen fit to make no mention of?

 Such a statement just makes me even more curious about what a properly conducted technical review will reveal. However, I won't be pre-ordering one on the rather tenuous basis that it might have such an enhancement alone. ;)

JBG
« Last Edit: July 12, 2019, 11:47:53 pm by Johnny B Good »
 

Offline bdunham7

  • Frequent Contributor
  • **
  • Posts: 330
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #28 on: July 12, 2019, 11:59:35 pm »
Sine waves don't have this jitter, so if you need a clock, try a sine wave. 

sine wave has exactly the same jitter. But sine wave has more slow slope, and this jitter is hidden behind slow slope. Since slope is too slow, amplitude change will be very small, so you will not see it in time domain. But you will see it on frequency domain.

If it hasn't already been said, the 4ns "jitter" is just the natural result of a 250 MSa/s fixed clock DDS putting out a square wave with a period that is not a multiple of 4ns. 

Such jitter will be "natural result" for DAC with fixed sample rate. But FY6900 has FPGA and can use any desired sample rate for DAC, so this is not the case for FY6900 hardware. FY6900 can produce signal with better jitter, just by using variable sample rate. Yeah it's a little bit more complicated, but it is possible and it's worth it. So, this jitter is just a software limitation in FPGA code and can be reduced by software patch.

I didn't fully understand your explanation, but your conclusion is incorrect both in fact and in theory.  The slope of a sine wave is absolutely no impediment to viewing jitter.  I can frequency modulate a carrier with a square wave (or just use FSK, I suppose) and it shows up just fine viewing just a few cycles.  I'm observing the zero crossing which can't be hidden or obscured!  In fact, the FY6600 I have produces obvious 4ns jitter of a binary variety--either one way or the other but not in between--for square waves and rectangular pulses of a period that is not a multiple of 4ns.  OTOH, almost every other waveform, including triangle and sine, does not have this type of jitter no matter how I observe it--a few cycles, many cycles on zoom, FFT, you name it.

The theory is simple:  Nyquist says that as long as I have a sample rate that is 2x (2.5x in practice) of my bandwidth, I can accurately reproduce my sine wave of any frequency within the bandwidth.  The key here is that my samples can be at any point on the sine wave and can vary in amplitude.  So, for a 9.999MHz sine wave, I get about 25 samples per cycle, but their position and amplitude can vary as needed.  Nyquist also says that due to their infinite bandwidth, you can never accurately reproduce a square wave with sampling, almost sort of, the exception being if the period each half of the square wave is an exact multiple of the sampling period.  The key, again, here, is that in a simple DDS system, the amplitude of the output samples is constrained between high and low.  When sampling a sine wave, a slight shift in the time domain yields a slight shift in the amplitude.  With square, it is all or nothing.  Thus the 4ns 'jitter' that we see is a phenomenon limited to functions with sharp transitions--square waves, pulses, single-ended ramps and so on.

I haven't dissected my FY6600 so I don't know if your assertion that it has all the necessary hardware for a variable sample rate is true.  I suspect it isn't, although I wouldn't rule out someone being clever enough to make it happen.  This limitation is common among most lower-end sig-gens and I'm sure this model is cut to the bone to make their price point.  The one cheap, simple way that has occurred to me is to use linear interpolation where if there is a transition within the 4ns period, that sample is interpolated time-wise to at least put the edge in more or less the right place.  Since this unit has ~7ns rise times anyway, an occasional 8ns or so rise time with the zero crossing in the right place would look a whole lot better.
 
The following users thanked this post: Jacon, Johnny B Good

Offline maxwell3e10

  • Frequent Contributor
  • **
  • Posts: 471
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #29 on: July 13, 2019, 01:00:09 am »
Until Agilent introduced Trueform technology in 2012 and other manufactures followed, most function generators suffered from the jitter problem if the frequency of a square waveform is not a multiple of the sample frequency.  So even the previous generation of Agilent generators, 33220 had a significant amount of jitter. The fact that you can now get a generator of similar performance for close to 1/100 of the price is quite impressive.
 
The following users thanked this post: Jacon, Johnny B Good

Offline bdunham7

  • Frequent Contributor
  • **
  • Posts: 330
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #30 on: July 13, 2019, 01:14:16 am »

 Seriously, you'd be better off imho, getting hold of the 6800 instead of the 6900 (but that 40 quid 6600 is such a bargain and the specification so identical to the 6800 it's hard to resist).  At that price, I couldn't resist buying myself a 'spare' but the one I ordered just on four weeks ago now is supposed to be arriving no later than today. I'll believe that when I see it. Fortunately, I'm not in any great hurry.

JBG



Did you ever get your unit from HK?
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #31 on: July 13, 2019, 02:16:29 am »
I didn't fully understand your explanation, but your conclusion is incorrect both in fact and in theory.  The slope of a sine wave is absolutely no impediment to viewing jitter.

your theory is wrong. It doesn't matter what kind of waveform you're using, the jitter is always here. But square and triangle wave has more high frequency components which affected by jitter much more. The main reason why you don't notice jitter for sine wave and notice it for square wave is slow slope of the sine wave.

The jitter is nothing more than time axis error for waveform point. You can see on the picture below that this time error depends on voltage error and vice versa. These errors on time axis and voltage axis are linked together.




When the slope of waveform is slower, the voltage axis error will be smaller for the same jitter. And vice versa, when the slope of waveform is faster, the voltage error will be higher for the same jitter. When you looking at sine waveform on oscilloscope, it has too slow slope in order to notice voltage error caused by jitter.

But the jitter is still there, you're just using wrong instrument to detect it. If you will use spectrum analyzer, you will see that the jitter for sine wave and for square wave is the same.

The theory is simple

for a 9.999MHz sine wave, I get about 25 samples per cycle

you can never accurately reproduce a square wave with sampling

When sampling a sine wave, a slight shift in the time domain yields a slight shift in the amplitude.  With square, it is all or nothing.

Yes, the theory is simple, and there is the same theory for sine wave and for square wave. A slight shift on the time axis yields a slight shift on the amplitude axis. But square wave has faster slope and this "slight shift" is more visible on that slope.

Let's don't talk about infinite spectrum of square wave, we don't need ideal square wave. We're need just a good square wave with a low jitter.

This jitter happens when you're trying to generate frequency which is not multiple of DAC sample rate frequency. In such case your signal doesn't fit DAC aperture, and some points will have floating error. And it doesn't matter if you're trying to generate sine or square wave. They both will have this jitter.

The solution here is to change DAC sample rate, in order to properly fit your wave with DAC aperture. For example if you're want to generate 9.999 MHz, you can change DAC sample rate from 250 MHz to 249.975 MHz and this jitter will disappears, just because 249.975 MHz / 25 = exactly 9.999000 MHz. ;)  Now the square wave exactly fits with DAC aperture and the reason for this jitter is removed.

The square wave will not be ideal, because it's spectrum is limited by analog bandwidth of the output amplifier and jitter of oscillator and different components (FPGA and DAC). But this jitter will be much more smaller and almost not noticeable.

This is not so easy to implement, because it needs to produce custom DAC sample rate and it should be low jitter. It requires to reconfigure PLL in FPGA at runtime, and it leads to use more complicated approach in FPGA software, but it is possible. The main complexity here for FPGA software is to get custom frequency with a low jitter.

Thus the 4ns 'jitter' that we see is a phenomenon limited to functions with sharp transitions--square waves, pulses, single-ended ramps and so on.

This 4 ns jitter is a result of fixed DAC sample rate. FY6600 has FPGA and there is not a big deal to use variable DAC sample rate. If you don't believe that FY6600 hardware allows to produce square wave with much-much lower jitter (almost not noticeable), you can check square wave at fequencies which are integer multiple of oscillator frequency. FY6600 already produces almost no jitter square wave at such frequencies  ;)
« Last Edit: July 13, 2019, 02:47:09 am by radiolistener »
 

Offline bdunham7

  • Frequent Contributor
  • **
  • Posts: 330
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #32 on: July 13, 2019, 03:06:58 am »
What we have here is failure to communicate.  :palm:

So instead of refuting your arguments, I'll just show you some pictures.  :popcorn:

The waveforms and statistics should be self explanatory.  The FFTs are in order: 9.8MHz sine wave, 10MHz square, 9.8MHz square (there's your jitter) and lastly a 9.615384MHz square which corresponds to a 104ns period.  I don't have the 10MHz sine FFT somehow but it wasn't much different than the first FFT, just a little less noisy. Last photo is a 10MHz sine wave with 4ns variation in period from 100us to 104us (using FSK modulation).  FSK and jitter aren't necessarily indentical concepts, but it is just to show that 4ns of period difference is certainly visible.
« Last Edit: July 13, 2019, 03:35:13 am by bdunham7 »
 
The following users thanked this post: rf-loop, Johnny B Good

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #33 on: July 13, 2019, 03:38:19 am »
Sine waves don't have this jitter, so if you need a clock, try a sine wave. 

sine wave has exactly the same jitter. But sine wave has more slow slope, and this jitter is hidden behind slow slope. Since slope is too slow, amplitude change will be very small, so you will not see it in time domain. But you will see it on frequency domain.

If it hasn't already been said, the 4ns "jitter" is just the natural result of a 250 MSa/s fixed clock DDS putting out a square wave with a period that is not a multiple of 4ns. 

Such jitter will be "natural result" for DAC with fixed sample rate. But FY6900 has FPGA and can use any desired sample rate for DAC, so this is not the case for FY6900 hardware. FY6900 can produce signal with better jitter, just by using variable sample rate. Yeah it's a little bit more complicated, but it is possible and it's worth it. So, this jitter is just a software limitation in FPGA code and can be reduced by software patch.

I didn't fully understand your explanation, but your conclusion is incorrect both in fact and in theory.  The slope of a sine wave is absolutely no impediment to viewing jitter.  I can frequency modulate a carrier with a square wave (or just use FSK, I suppose) and it shows up just fine viewing just a few cycles.  I'm observing the zero crossing which can't be hidden or obscured!  In fact, the FY6600 I have produces obvious 4ns jitter of a binary variety--either one way or the other but not in between--for square waves and rectangular pulses of a period that is not a multiple of 4ns.  OTOH, almost every other waveform, including triangle and sine, does not have this type of jitter no matter how I observe it--a few cycles, many cycles on zoom, FFT, you name it.

The theory is simple:  Nyquist says that as long as I have a sample rate that is 2x (2.5x in practice) of my bandwidth, I can accurately reproduce my sine wave of any frequency within the bandwidth.  The key here is that my samples can be at any point on the sine wave and can vary in amplitude.  So, for a 9.999MHz sine wave, I get about 25 samples per cycle, but their position and amplitude can vary as needed.  Nyquist also says that due to their infinite bandwidth, you can never accurately reproduce a square wave with sampling, almost sort of, the exception being if the period each half of the square wave is an exact multiple of the sampling period.  The key, again, here, is that in a simple DDS system, the amplitude of the output samples is constrained between high and low.  When sampling a sine wave, a slight shift in the time domain yields a slight shift in the amplitude.  With square, it is all or nothing.  Thus the 4ns 'jitter' that we see is a phenomenon limited to functions with sharp transitions--square waves, pulses, single-ended ramps and so on.

I haven't dissected my FY6600 so I don't know if your assertion that it has all the necessary hardware for a variable sample rate is true.  I suspect it isn't, although I wouldn't rule out someone being clever enough to make it happen.  This limitation is common among most lower-end sig-gens and I'm sure this model is cut to the bone to make their price point.  The one cheap, simple way that has occurred to me is to use linear interpolation where if there is a transition within the 4ns period, that sample is interpolated time-wise to at least put the edge in more or less the right place.  Since this unit has ~7ns rise times anyway, an occasional 8ns or so rise time with the zero crossing in the right place would look a whole lot better.

 Thank you bdunham7,

 That explanation neatly explains why the 4ns jitter is totally absent from sine waves and anything else based on sine waves. Whilst I had the wonderfully explained reasons why a bandwidth limited signal doesn't produce stair steps when digitised and converted back to analogue in this excellent video presentation in mind which, for anyone who hasn't already watched it, is well worth viewing:-



 I just had to run my own tests to confirm these facts for myself, just in case the function generator was doing something strange and wonderful in its processing of stored waveforms. The key to the matter of this sampling jitter on sharp edged pulses that you unearthed is the fact that they involve a theoretically infinitely fast transition between two levels at least once per cycle.

 This was precisely what I saw when trying successive waveforms one by one. Anything involving a sine curve such as all of the rectified sine wave examples whether full or half wave, as well as the triangle and the Sinc-pulse waveform, were completely devoid of the 4ns jitter that plagues all rectangular wave forms and ramps with an instant transition at the start or end of the ramping up or down period.

 Interestingly, I'm seeing rise/fall times of 3.8ns +/-200ps or so on the Sinc-Pulse and the buffered output from the GPSDO's OCXO. Considering such fast rise/fall times on the Sinc-Pulse waveform, it looks as though Feeltech (as they were calling themselves at the time) could have cheated their way out of this 4ns jitter issue rather like Siglent had done with their own dual channel DDS function generators (just take a look at their own 'scope traces demonstrating the elimination of the jitter of an earlier model - the 'cured trace' looks like all they've done is to smear out the rise/fall times to disguise the problem).

 If a sine based pulse can demonstrate such a fast rise and fall time as better than 4ns without any hint of the 4ns jitter that plagues the square wave, it strikes me that they could simply treat such waveforms as an imperfect square wave with a 4 or 5ns rise time limit before being processed by the DAC rather than have the DAC attempt the impossible task of generating an infinitely fast transition of which it has no control of in regard of its exact desired timing.

 Since there's a low pass anti-aliasing filter with something like a 75MHz cut off frequency[Edit; it might even be as high as 100MHz - still below the 125MHz Nyquist frequency in this case- since square waves as high as 30MHz are still recognisably a bandwidth limited square wave when displayed on a 200MHz BW 'scope] in the path, the highest "square wave" frequency you can hope to put out that still has a vague resemblance to such would be just 25MHz[Edit; 30MHz] at a pinch. Imposing a rise/fall time limit of 8ns would be the least of such a square wave's problems at that upper frequency limit so would 'cure the 4ns jitter without too much compromise. If it works for Siglent, then why not? Perhaps I'm taking too simplistic a view of the problem but the Sinc-Pulse evidence would suggest not. :-//

 If the cure is as simple as I've hypothesised and Feelelec have applied a firmware update to do exactly that, then the new iteration of the FY6*** series may well be worth considering as an upgrade. However, if that were the case, you'd expect Feelelec to be boasting this feature rather than the 24Vpp in the 0 to 5MHz range feature of somewhat dubious worth.

 I've said this before but it will be interesting to see a full review of this 'new and improved' model when it finally does hit the market or preview samples are issued to selected and privileged reviewers.

JBG
« Last Edit: July 13, 2019, 07:42:43 pm by Johnny B Good »
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #34 on: July 13, 2019, 03:44:29 am »
So instead of refuting your arguments, I'll just show you some pictures.  :popcorn:

As you can see, your pictures with FFT (even despite the fact that it has too low resolution and a lot of aliases) shows that the jitter is present on both waveforms - sine wave and on sqare wave. You can see that jitter as a more taller "grass" and "Christmas Tree" around the fundamental component in frequency domain.  :)

And you can see that 10 MHz square wave has no jitter. I mean noticeable 4 ns jitter that we're talking about. Yes, it always has some small jitter, some picoseconds or something like that, but it is not so bad as 4 ns.

This is because 10 MHz can be taken with integer divider (with no fraction part) from used DAC sample rate frequency. 9.8 MHz cannot be taken with integer divider from DAC sample rate frequency, it leads to fraction part. This fraction part leads to floating error on time axis, which is nothing else than our 4 ns jitter on oscilloscope.

You can eliminate this jitter on 9.8 MHz square wave just by change DAC sample rate. For example, if you change DAC sample rate to 196 MHz, your 9.8 MHz square wave will be jitter free. Because 196 MHz / 20 = exactly 9.800000 MHz with no fraction part.

Do you still think that it's impossible to synthesize 196 MHz on FPGA PLL? :)
« Last Edit: July 13, 2019, 03:48:16 am by radiolistener »
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #35 on: July 13, 2019, 04:05:57 am »

 Seriously, you'd be better off imho, getting hold of the 6800 instead of the 6900 (but that 40 quid 6600 is such a bargain and the specification so identical to the 6800 it's hard to resist).  At that price, I couldn't resist buying myself a 'spare' but the one I ordered just on four weeks ago now is supposed to be arriving no later than today. I'll believe that when I see it. Fortunately, I'm not in any great hurry.

JBG



Did you ever get your unit from HK?

 Nah, and it's now 10 days overdue on the latest of the estimated dates of delivery. I sent the dealer a message to alert them of the delay via Ebay's notification system a couple of days ago. I now see they did respond late Friday afternoon with the following message:

'dear customer, We sent the item by the ordinary mail way and it only has a little tracking information .Since you still haven’t received it till now, I think it may be delayed in transit or lost on the way. But please don’t worry, we will be fully responsible, and we will send you a new parcel for free. But if you receive two parcels finally, would you please refused one or pay for the second item ,is this fine with you? Many thanks! Best wishes '

 I'm a little dubious about being able to refuse a second parcel after the original or second parcel finally turns up. I only need the one 'spare generator', owning two 'spares' would, to my mind,  be gilding the lily somewhat. This is a situation I've never had to deal with before. Presumably refusing delivery on a second unwanted item is perfectly normal practice in these cases?  :-//

 It might, for all I know turn up in Saturday's post and I'll be able to save the dealer the trouble of sending a second unit. Interestingly, that 99p order, after I discovered the Parcelmonitor web site to submit its tracking number to, has been languishing in customs processing, Hong Kong since the 1st of June and, apparently is still there as I type this reply. :wtf:
The only thing to be said in its favour is that it isn't actually overdue on its latest delivery date (25/07/19). ::)

 I'll report on the firmware version as soon as I get hold of my 'bargain signal generator', whenever that might be.

JBG
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #36 on: July 13, 2019, 04:21:06 am »
4ns jitter is totally absent from sine waves and anything else based on sine waves

this 4 ns IS PRESENT on sine wave, but you don't see it on oscilloscope, because sine wave has too slow slope. You're need to use higher frequency sine wave in order to see it on oscilloscope. Or just use spectrum analyzer, it will show you this jitter (as parasitic spectral components) for sine wave on any frequency.

This picture will explain you why this 4 ns jitter is present on sine wave, but you don't notice it on oscilloscope:
« Last Edit: July 13, 2019, 04:24:12 am by radiolistener »
 

Offline bdunham7

  • Frequent Contributor
  • **
  • Posts: 330
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #37 on: July 13, 2019, 04:49:46 am »
@ JBG:  What is your maximal delivery date?  Mine is Aug 07, with a range of Jun 26 to Aug 07 given.  If it goes over that maximal date, you need to file a not-received report with eBay and resolutely ignore any pleas from the seller to accept a second shipment or a refund through PayPal outside the eBay process. I've worried about non-shipment since day one.

@radiolistener:  I've no idea what to say. :-//  I've clearly demonstrated the ability to see 4ns period deviation on a sine wave (last photo).  The FFTs are fine for what they are and pretty clearly show what I want them to.  Yes, there is jitter on all of the waveforms, but the 9.8MHz square wave clearly stands out both in the FFT and in the measurments.  And if you look at the statistics under the waveforms the 9.8MHz square wave is showing a 1.75ns width deviation and 160ps std deviation on period.  All the other period deviations are in the 10s of nanoseconds.  The deviation numbers on the square wave go up by a factor of 7-8 when you go from 10.0 to 9.8 MHz.  The number for the sine wave go up by maybe 30%, so maybe there are issues with sample interpolation producing distortion in the sine wave--but it doesn't have a 4ns problem. 
 
The following users thanked this post: rf-loop

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #38 on: July 13, 2019, 05:01:37 am »
bdunham7, if you think that small voltage error due to this 4 ns jitter will not affects your measurements much, it's a delusion.

In theory such 14 bit DAC should produce 9.8 MHz sine wave with about SNR=86 dB (it takes into account average DAC DNL and effective DAC noise and zero jitter). This is what should be with zero jitter.

But jitter will leads to SNR degradation. For example 4 ns RMS jitter for 9.8 MHz sine wave will leads to SNR=12 dB.
The difference is 74 dB!

74 dB of dynamic range is lost just due to 4 ns jitter! And this is for sine wave.  ;)


if you look at the statistics under the waveforms the 9.8MHz square wave is showing a 1.75ns width deviation and 160ps std deviation on period.

For calculations I assumed 14 bit DAC with average DNL = 0.41 LSB and effective output noise of DAC = 0.9 LSB.

The theory says that 160 ps RMS jitter for 9.8 MHz sine wave will leads to SNR = 40.1 dB.

This pretty well correspond to these parameters that we seen in reality for FY6600.

But the difference with zero jitter DAC is 45.91 dB!
The loss of 46 dB dynamic range is too much.
« Last Edit: July 13, 2019, 06:39:20 am by radiolistener »
 

Offline bdunham7

  • Frequent Contributor
  • **
  • Posts: 330
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #39 on: July 13, 2019, 05:15:28 am »
So look at the pictures and tell me how they agree or disagree with your theoretical explanations. 
 
The following users thanked this post: rf-loop

Offline pantelei4

  • Regular Contributor
  • *
  • Posts: 90
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #40 on: July 13, 2019, 05:23:57 am »
this 4 ns IS PRESENT on sine wave, but you don't see it on oscilloscope, because sine wave has too slow slope.
dV/dT limited by output amplifier
At high frequency, the slope of the output meander and the sine is the same. But there is no 4 ns jitter visible on the sine, even at high sensitivity.

 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #41 on: July 13, 2019, 05:35:38 am »
So look at the pictures and tell me how they agree or disagree with your theoretical explanations.

Theory predicts SNR = 40 dB at 9.8 MHz sine wave for RMS jitter 160 ps (it's your measurement for 9.8 MHz square wave).

Your picture shows a little worse performance, at 9.8 MHz SNR is about 25 dB or something like that.
The worse performance in reality can be explained by not enough precision of your equipment.
Probably RMS jitter is more than 160 ps at 9.8 MHz.
According to your pictures RMS jitter is about 900 ps.
And in overall my theoretical explanation pretty well corresponds with your pictures.  :)
« Last Edit: July 13, 2019, 06:00:36 am by radiolistener »
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #42 on: July 13, 2019, 05:40:26 am »
At high frequency, the slope of the output meander and the sine is the same. But there is no 4 ns jitter visible on the sine, even at high sensitivity.

that's interesting information. May be this is because FPGA trying to apply interpolation for sine wave and the result is then filtered with analog bandwith, but for square wave it just puts max and min values with no interpolation?

Interpolated points is more close to real sine in comparison with min/max value with no interpolation. If so, then this is the second bug in the FPGA software.

Any other ideas how it is possible?
« Last Edit: July 13, 2019, 05:51:39 am by radiolistener »
 

Offline pantelei4

  • Regular Contributor
  • *
  • Posts: 90
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #43 on: July 13, 2019, 05:48:41 am »
May be this is because FPGA trying to apply interpolation for sine wave and the result is then filtered with analog bandwith, but for square wave it just puts max and min values with no interpolation?
Yes, interpolation for the front of the meander is impossible and this is the max and min values
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #44 on: July 13, 2019, 05:56:53 am »
Yes, interpolation for the front of the meander is impossible and this is the max and min values

I think it is possible, but is more hard, we're need to take into account the actual analog bandwidth for calculations.
Because if we ignore analog bandwidth we will get much higher error.
 

Offline pantelei4

  • Regular Contributor
  • *
  • Posts: 90
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #45 on: July 13, 2019, 06:02:27 am »
I think it is possible, but is more hard, we're need to take into account the actual analog bandwidth for calculations.
Probably they do this in more advanced DDS, taking into account the bandwidth of the analog output, interpolation of the fronts of the meander occurs.
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #46 on: July 13, 2019, 06:13:13 am »
yeah, implementing such features requires a lot of math and more complicated software, also it makes sense to use better analog frontend, so it is not for entry level device :)

But may be sometimes we will see it in cheap FY7000 or something like that  :D
« Last Edit: July 13, 2019, 06:15:43 am by radiolistener »
 

Offline pantelei4

  • Regular Contributor
  • *
  • Posts: 90
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #47 on: July 13, 2019, 06:22:14 am »
yeah, implementing such features requires a lot of math and more complicated software
It does not require, it is necessary only once to compile an interpolation table of the slope of the pulse fronts in accordance with the analog band
That's the whole secret of MagicPulse
« Last Edit: July 13, 2019, 06:24:14 am by pantelei4 »
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #48 on: July 13, 2019, 05:10:37 pm »
@ JBG:  What is your maximal delivery date?  Mine is Aug 07, with a range of Jun 26 to Aug 07 given.  If it goes over that maximal date, you need to file a not-received report with eBay and resolutely ignore any pleas from the seller to accept a second shipment or a refund through PayPal outside the eBay process. I've worried about non-shipment since day one.


 24th of June till the 3rd of July. As I said, it was already a week overdue on the final date when I used Ebay's "Send a Request" to inform the dealer of the delay. The response two days later seems quite reasonable, especially after having a good night's sleep to refresh my rather tired state of mind when I first read it.

 As far as I can see, they're offering to send a second parcel straight away in the event that the original cannot be immediately located and accounted for in the postal system. Requesting that if a second parcel finally lands on my doorstep that I refuse it and ensure its return with the option to pay for it (presumably also at half price) if I so desire to have a second 'cheap spare'. Since one "cheap spare" is more than enough, I won't be availing myself of that option.

 It's obvious that they've chosen the cheapest, non tracked (presumably also uninsured) option by the cheapest carrier on the basis that such loss events are statistically rare enough to forego the expense of a tracked and insured posting option for it to be cheaper to resolve such failures by simply shipping out a replacement at their own cost rather than pay a higher premium to make the carrier take full responsibility for any such losses. It's known as 'Playing the Odds'.

 This is all fine and dandy, provided they remember to bribe their luckless customer into doing repeat business and not badmouth them for the additional delay on top of the already excruciating delay even when delivery times are actually met. I'll accept their offer but only on the basis that they offer some financial compensation for the late delivery and their assurance that the firmware is version 3.3 or above.

 I notice that they are now asking 80 quid for the FY6600-60M models (double the price I'd paid) so I'd rather receive the goods at that price or not at all. If I cancel the order, I'll lose out on my "Half price Bargain". Since I'm not in any desperate hurry to acquire a spare unit, it seems my best option is to accept their solution and hope they take my request for assurance of the firmware version and a modicum of recompense for the extra delay (33 to 50 percent off ???) seriously. I haven't responded yet so I'll see what concessions I can wring out of them.

[EDIT]

 I've just sent this message via Ebay's request system.

Thank you for the offer. Before I accept, can you assure me that the item is not old stock cursed by firmware versions 3.0 and 3.1 which caused them to be rendered unusable? It needs to be at version 3.3 or above. Also, as is normal in these cases, will you be offering some discount by way of recompense for the inconvenience of this additional delay?

 Hopefully, I'll get a favourable response ("Nothing ventured, nothing gained." and all that...), and all under auspices of Ebay's "Send a Request" system which gives me the option to escalate it to Ebay on or after the 19th.

BTW, that little 99p pack of HC14s are still stuck in HK customs. They've been there since the 1st of June!!! However, the latest date of arrival is still some 12 days off so I can't do anything about that one just yet (it's still 'early days'... after six weeks! :(

JBG

« Last Edit: July 13, 2019, 06:28:41 pm by Johnny B Good »
 

Offline bdunham7

  • Frequent Contributor
  • **
  • Posts: 330
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #49 on: July 13, 2019, 07:48:44 pm »
I  think it pays to be a little more hard-hearted with sellers.  You have 30 days from the last delivery date to file INR, and some of these guys will say anything to try and run the clock out.  This is seller honghong20, right?  I haven't received mine nor you yours, so I think it is possible that no packages have been sent.  Talk of refusing packages is pretty strange--you should NEVER refuse a package according to eBay--and the seller wouldn't want to incur the return shipping charges that would likely exceed the value of the transaction.
 
The following users thanked this post: gnavigator1007, Johnny B Good

Offline bdunham7

  • Frequent Contributor
  • **
  • Posts: 330
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #50 on: July 13, 2019, 08:21:51 pm »
So look at the pictures and tell me how they agree or disagree with your theoretical explanations.

Theory predicts SNR = 40 dB at 9.8 MHz sine wave for RMS jitter 160 ps (it's your measurement for 9.8 MHz square wave).

Your picture shows a little worse performance, at 9.8 MHz SNR is about 25 dB or something like that.
The worse performance in reality can be explained by not enough precision of your equipment.
Probably RMS jitter is more than 160 ps at 9.8 MHz.

According to your pictures RMS jitter is about 900 ps.
And in overall my theoretical explanation pretty well corresponds with your pictures.  :)

I don't think your jitter math will work here as you would expect.  First, we should define jitter, which could involve the generator sample clock, the scope/FFT trigger gate or the DDS process itself.  I am considering the jitter to be the variation in the timing of the rising edge of the waveform at the zero crossing point.  I've previously used quote marks to refer to the 4ns "jitter" because although it is based on a random displacement of the transition by +/- 2ns, it really isn't jitter as measured by the scope or as it would be seen by most devices looking at a clock signal.  How this 4ns sample spacing constraint affects the output varies wildly with frequency.

You shouldn't infer that all of the things you see on the FFT are a result of jitter (as I've defined it) or that a certain s/n ratio implies a certain level of jitter.  I think the variation if the falling edge of a square wave due to the 4ns effect is better characterized as distortion--but I'm not sure characterizing it helps us understand it any better.

Look at the 10 MHz square wave photos.  The period and width variations are pretty low, but on the FFT, in addition to the expected odd harmonics, you see peaks at 0, 20 and 40MHz.  Why?  Simple--even though the signal period is a multiple of 4ns, the expected falling edge transition occurs exactly in between samples, since 50/4=12.5.  The FY6600 makes the best of it by simply having the high period be consistently 48ns and the low 52ns--or a 48% duty cycle if  you will.  That's good for low jitter clock signal, but it bad for spectral purity--it causes the even harmonics and an 8% or so average DC offset.

So in the 9.8MHz case, jitter (as defined by me and as measured by the scope) goes up because the leap-nanosecond method doesn't yield uniform results, but it is still much closer than I expected.  However, every cycle of the waveform will be different than the last as far as the width the high and low periods and you get the result you see, which is the 2ns or so of pseudo-random variation in duty cycle .  That's not an equipment fault, this FFT can show clean single frequency peaks with a dynamic range of 80db or so.  In any case, the bulk of the pseudo-noise you see on the FFT is caused by the variation in the duty cycle from period to period, which I would characterize as harmonic distortion--but I'm open to better terminology if anyone has an idea.

Now the sine waves just don't have this particular issue.  You can see that the upper and lower halves of both sine waves have identical durations that are not multiples of 4ns.  I'm not saying the sine waves are perfect--they seem to have 65-70db noise floors.  This may be due to sample clock jitter, the DDS method used (linear interpolation?) or DAC non-linearity.  What they don't have is any evidence of the 4ns effect.
« Last Edit: July 13, 2019, 10:48:50 pm by bdunham7 »
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #51 on: July 13, 2019, 09:51:16 pm »
4ns jitter is totally absent from sine waves and anything else based on sine waves

this 4 ns IS PRESENT on sine wave, but you don't see it on oscilloscope, because sine wave has too slow slope. You're need to use higher frequency sine wave in order to see it on oscilloscope. Or just use spectrum analyzer, it will show you this jitter (as parasitic spectral components) for sine wave on any frequency.

This picture will explain you why this 4 ns jitter is present on sine wave, but you don't notice it on oscilloscope:

 Hi radiolistener,

 That's a very nice picture you've provided. However, it does seem to be based on a false premise. I've looked quite closely at the sine wave zero crossing points. Increasing the Y amplifier gain is an effective way to steepen up the flanks of any waveform to unmask any such hidden DAC clock jitter artefacts. At best, all I can see is the usual random jitter noise present on all wave forms.

 Only square waves and all others which likewise include a fast edge transient, have exhibited this DAC clock jitter artefact. If you possess one of these Feeltech signal/function/Arbitrary Wave generators (FY66/6800), a simple experiment can demonstrate these observations made by both bdunham7 and myself.

 There's no need for a separate 10MHz high precision reference (that just adds another dimension to the observations), nor does the generator have to be upgraded to a better 50MHz clock oscillator. You simply set the frequency to 10MHz exactly and then apply a 10mHz offset which will effectively provide a strobing effect to reveal the 4ns jitter in slow motion. The signal generator's 50MHz clock doesn't even need to be calibrated, the results will be the same regardless.

 Having set the frequency, you can now work your way through as many wave forms as you care to examine. You will need to observe each one for at least ten seconds at a time. You will also need to display several cycles worth on the 'scope display. For a ten MHz frequency, this means a setting around the 50ns per division mark in most cases.

 If you can run this simple experiment, I'd be quite interested in your own conclusions as to what is actually happening. Mine for the most part are based on the basic theory of digitising analogue wave forms in a bandwidth limited system whose upper frequency limit resides below the Nyquist frequency limit.

 All of the wave forms which don't include fast transient edges requiring in theory infinite bandwidth can be conveniently stored as an "Arbitrary Wave form" and clocked out at any frequency without distorting the waveshape since such waves (sines, triangles and other similarly curved waveforms free of any infinitely fast transients) are entirely scalable in their wave shape in both amplitude and their time base.

 However, when it comes to the other wave forms possessed of a theoretically perfect infinitely fast transient such as ramps and square/rectangle waves where a less than perfect 7ns rise/fall time compromise has to be accepted, these must be being handled in a completely different way in order that the rise/fall times remain at 7ns regardless of their fundamental frequency (strictly, repetition rate) whether it's one milliHertz or ten MHz.

 Since I'm no expert in DDS technology, nor have I studied it in any depth, I can only guess that such sharp edged waveforms which need to preserve  fixed rise and fall times regardless of repetition rate (frequency) are handled outside of the bandwidth/Nyquist frequency limited digital processing of the less demanding stored waveforms.

 Since the stored arbitrary waveforms which have no such conflicting requirement to generate edges with a fixed rise/fall time regardless of frequency don't suffer from the 4ns jitter, courtesy of the bandwidth limited processing, you might imagine that storing a square wave as an arbitrary wave with a 7ns rise/fall on a 30MHz representation would solve the problem but a moment's consideration will tell you that when such a waveform is clocked out to produce a 3MHz square wave, it will have rise/fall times of 70ns, scaling to 700ns at 300KHz and a whopping 70μs at 3KHz.

 Quite obviously, this idea is a non-starter. The method actually being used by Feeltech to preserve a 7ns rise and fall time at all frequencies has come with the less contentious penalty of a 4ns jitter which is a very respectfully low level of jitter compared to what was being accepted in high end professional test equipment costing hundreds of times more only a decade ago.

 The jitter issue in such a cheap signal generator, clearly aimed at the hobbyist market, is not a deal breaker. In many cases it'll have little to zero impact on their use. In the rare cases where it does, most resourceful hobbyists will be able to cost effectively apply the work arounds that were once practised by the professionals only a decade or so back when their ten thousand dollar kit fell short of the tasks they were being put to.

 At the end of the day, you get what you pay for and these Feeltech products give you a surprisingly large amount of value for your money. As to whether or not Feeltech / Feelelec have applied a firmware update to mitigate the 4ns jitter issue remains to be seen. In view of the lack of any mention of such a radical upgrade, I rather doubt it.

JBG
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #52 on: July 13, 2019, 10:53:03 pm »
First, we should define jitter, which could involve the generator sample clock, the scope/FFT trigger gate or the DDS process itself.

I'm talking about total jitter of entire generator, which includes jitter sum of all it's components:

total_jitter  = sqrt( oscillator_jitter^2 + FPGA_jitter^2 + DAC_jitter^2 + NCO_jitter^2 +.... )

How this 4ns sample spacing constraint affects the output varies wildly with frequency.

yes,and this is why I calculated SNR degradation due to the jitter at specific frequency 9.8 MHz. On higher frequency it will be worse.

You shouldn't infer that all of the things you see on the FFT are a result of jitter (as I've defined it) or that a certain s/n ratio implies a certain level of jitter. 

FFT includes fundamental, harmonics and spurs caused by jitter and non-linearities at analog frontend. Also it includes aliases of all these components which doesn't fit into first Nyquist zone of your scope.

Look at the 10 MHz square wave photos.  The period and width variations are pretty low, but on the FFT, in addition to the expected odd harmonics, you see peaks at 0, 20 and 40MHz.  Why? 

Usually such components is a result of even-order nonlinearities in analog frontend. Such non-linear distortion can be caused by saturated MOSFET, diode or something like that. The better analog frontend, the smaller will be these components.

So in the 9.8MHz case, jitter (as defined by me and as measured by the scope) goes up because the leap-nanosecond method doesn't yield uniform results, but it is still much closer than I expected. 

When your output frequency is divided from DAC sample rate with fractional part, there always will be jitter. Just because your frequency doesn't fit to DAC aperture. It doesn't matter - sine, cosine, square or triangle wave. Because problem in time rounding error and this problem is the same for any kind of waveform with specific frequency. You cannot fix this issue at fixed DAC sample rate.

In any case, the bulk of the pseudo-noise you see on the FFT is caused by the variation in the duty cycle from period to period, which I would characterize as non-harmonic distortion--but I'm open to better terminology if anyone has an idea.

Jitter always produces spurs and noise around fundamental.  And they are not "pseudo", they are real, and they are really present in the signal.


Now the sine waves just don't have this particular issue.

On your sine FFT I see spurs and grass around fundamental, they are product of jitter. And it should exists for any kind of waveform with frequency which divided from DAC sample rate with a fractional part.
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #53 on: July 13, 2019, 11:08:24 pm »
That's a very nice picture you've provided. However, it does seem to be based on a false premise. I've looked quite closely at the sine wave zero crossing points. Increasing the Y amplifier gain is an effective way to steepen up the flanks of any waveform to unmask any such hidden DAC clock jitter artefacts. At best, all I can see is the usual random jitter noise present on all wave forms.

You cannot deceive nature and invent a perpetual motion machine.
In the same way you cannot deceive nature and produce jitter free sine wave which is clocked from the source with jitter.

The jitter doesn't linked to waveform, it is linked to time error. The jitter will be exactly the same for any kind of waveform. Because time error doesn't depends on waveform, it depends the fundamental frequency and DAC sample rate relation. You cannot eliminate it at fixed sample rate. It doesn't matter what kind of waveform you will use, the jitter will be there...

« Last Edit: July 13, 2019, 11:10:01 pm by radiolistener »
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #54 on: July 13, 2019, 11:26:31 pm »
I  think it pays to be a little more hard-hearted with sellers.  You have 30 days from the last delivery date to file INR, and some of these guys will say anything to try and run the clock out.  This is seller honghong20, right?  I haven't received mine nor you yours, so I think it is possible that no packages have been sent.  Talk of refusing packages is pretty strange--you should NEVER refuse a package according to eBay--and the seller wouldn't want to incur the return shipping charges that would likely exceed the value of the transaction.

 Thanks for that worrying advice (I think :-//).

 I've only ever communicated via Ebay's INR Request system which advised me to try and resolve a solution with the trader and telling me I could raise the issue on the 19th if not resolved to my satisfaction by then.

 I've seen mentions of delaying tactics being used by some Ebay traders so I am mindful of the issue. In this case, we're dealing with different traders (although possibly the same under two different names). I'm dealing with a trader with the name of "hgfurniture2018",  "Based in China, hgfurniture2018 has been an eBay member since 09 Jun, 2018", so just over a year in business. His feedback score is 4608 with a 98.6% positive Feedback rating.

 I know that feedback ratings generally need to be larger than 99.8% to instil full confidence and I'm not sure whether a 13 month trading history is long enough to reduce the risk of a fly by night disappearing act being pulled - is it long enough?

 Do Ebay monitor these negotiations or do you have to explicitly describe them when seeking their assistance? The email from Ebay suggests they're aware of the content of these communications so, maybe they do record them for 'posterity' to help resolve any disputes. :-// If Ebay advise against refusing a delivery, that request should raise alarms if not an eyebrow or two.

 I've replied to their suggested remedy with caveats of my own so I'm now awaiting their response before I query with Ebay their request that I refuse a second package turning up after they've sent a replacement to see if this is an acceptable action in this circumstance.

JBG
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #55 on: July 13, 2019, 11:29:35 pm »
Quite obviously, this idea is a non-starter. The method actually being used by Feeltech to preserve a 7ns rise and fall time at all frequencies has come with the less contentious penalty of a 4ns jitter which is a very respectfully low level of jitter compared to what was being accepted in high end professional test equipment costing hundreds of times more only a decade ago.

This is just totaly wrong approach (to preserve 7 ns rise time in cost of spectral purity). This is the same as to perform sample rate reduction by using decimation with no filtering at all. It will leads to aliases, it is very known issue. The same thing happens here. This increased jitter on square wave is a result of missing filter (interpolation). And it leads to a jitter (aliases).

The picture from pantelei4 shows that jitter for square wave is much higher than it should be.

If it looks as more sharp slope on the oscilloscope, it doesn't means that it's better. Because such signal consists of additional non-harmonic frequencies and they will affect circuit where you planning to use such pseudo-square wave.

The only way to get more clean and better quality signal on the output is to use interpolation. Any other attempts, such as trying to "make 48% duty cycle", "preserve 7 ns rise time" are completely wrong and will leads to dramatic non-linear distortions. And these non-linear distortions are much worse than "smooth square wave" visual effect on oscilloscope.

There is nothing bad with "smooth square wave". This is completely normal. Because it is limited by analog bandwidth. You cannot make more wide bandwidth by using these tricks. All what you get is just non-linear distortions. Which is the real problem.

If FY6600 really uses such "tricks", like "48% duty cycle" and "preserve 7 ns rise time" then this is complete crap.

I am more inclined to believe that this is more a software mistake than a deliberate use of such bullshit.
« Last Edit: July 14, 2019, 12:07:59 am by radiolistener »
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #56 on: July 14, 2019, 12:06:50 am »
That's a very nice picture you've provided. However, it does seem to be based on a false premise. I've looked quite closely at the sine wave zero crossing points. Increasing the Y amplifier gain is an effective way to steepen up the flanks of any waveform to unmask any such hidden DAC clock jitter artefacts. At best, all I can see is the usual random jitter noise present on all wave forms.

You cannot deceive nature and invent a perpetual motion machine.
In the same way you cannot deceive nature and produce jitter free sine wave which is clocked from the source with jitter.

The jitter doesn't linked to waveform, it is linked to time error. The jitter will be exactly the same for any kind of waveform. Because time error doesn't depends on waveform, it depends the fundamental frequency and DAC sample rate relation. You cannot eliminate it at fixed sample rate. It doesn't matter what kind of waveform you will use, the jitter will be there...

 Yes, agreed, there'll always be some level of jitter (along with many other sources of imperfection in the DAC process). However, those residual effects aren't what's being discussed here, We're rather more concerned with the gross effects of the 4ns DAC clock jitter that afflicts the square wave and its close cousins in the waveform zoo when the frequencies selected aren't an exact multiple of the DAC clock frequency.

 Since you haven't responded to my suggestion to examine what actually happens when you run some basic tests with an FY6600 or FY6800, I'm assuming you don't actually have either in your possession to run these tests (I'm assuming you do at least have a suitable 'oscilloscope to run such tests).

 When it comes to hypothesis versus experiment, experiment trumps hypothesis every time. If you're arguing purely from the basis of theory or a hypothesis without any experimental observations to back up your assertion, then I'd prefer you to hold back on your advice until you do have some experimental results to back up your claims which, quite frankly are at odds with what is actually observed in practice. IOW, put up or shut up. >:(

JBG
 

Offline bdunham7

  • Frequent Contributor
  • **
  • Posts: 330
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #57 on: July 14, 2019, 12:12:02 am »
That's a very nice picture you've provided. However, it does seem to be based on a false premise. I've looked quite closely at the sine wave zero crossing points. Increasing the Y amplifier gain is an effective way to steepen up the flanks of any waveform to unmask any such hidden DAC clock jitter artefacts. At best, all I can see is the usual random jitter noise present on all wave forms.

You cannot deceive nature and invent a perpetual motion machine.
In the same way you cannot deceive nature and produce jitter free sine wave which is clocked from the source with jitter.

The jitter doesn't linked to waveform, it is linked to time error. The jitter will be exactly the same for any kind of waveform. Because time error doesn't depends on waveform, it depends the fundamental frequency and DAC sample rate relation. You cannot eliminate it at fixed sample rate. It doesn't matter what kind of waveform you will use, the jitter will be there...

So here is where you are going wrong.  >:D

First, Nyquist says that I can PERFECTLY reproduce a sine wave (in theory) as long as my sample rate is more than 2x the fundamental frequency and my output filter completely removes all bandwidth above the Nyquist frequency.  In reality, of course, it is easier to use a higher sample rate because the output filters can be made more easily.

Second, the fact that the sample rate is not a multiple or factor of the frequency is completely irrelevant.  It can be ANY NUMBER more than 2X.  A sample rate that is not related to the frequency is NOT jitter.  All I have to do is accurately solve the equation f(x) = (amplitude * sin (frequency * 2 *pi *x)) with the appropriate constants for each sample point and my output will be perfect.

Third, even your assertion that you can't get a perfect sine wave from a clock with jitter is wrong, although in practice it would generally be true.  If you apply a technique used in Equivalent Time Sampling on some DSOs, you can have the samples at a more or less random rate (as long as it always exceeds Nyquist) as long as you are able to accurately measure the exact timing of the sample and apply the calculation to that time.  Obviously, if you expect the samples at one time but they occur at another, you have an error.  So if your calculations are based on exact 4ns samples and they occur at 4ns +/- 0.5ns, you'll have jitter. 

You keep mentioning the "grass" around my signal on the FFT.  Yes, it's a bit noisy and I suppose some of it is sample clock jitter.  The FY6600 apparently doesn't shine in the clock department.  But I suspect that some of that is also that they are using a cruder interpolation to translate a stored sine wave rather than calculating 250 million sine functions per second on the fly.  But all in all it isn't a bad signal for a low-end machine and the sine noise is nowhere near what the square wave had.

And why, I have to ask, are you telling me that those very pronounced second and fourth harmonics on the 10MHz FFT are from a non-linearity in the analog section when they don't appear elsewhere and I clearly explained what causes them in this case?  Do you think my explanation is wrong?
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #58 on: July 14, 2019, 12:17:42 am »
I'm assuming you don't actually have either in your possession to run these tests

yes, I don't have it, I planned to buy it, but later changed my decision because of this issue with jitter which is reported by other users. I thought this is just DAC aperture jitter. But pantelei4 shows that there is much worse issue with jitter.
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #59 on: July 14, 2019, 02:26:35 am »
First, Nyquist says that I can PERFECTLY reproduce a sine wave (in theory) as long as my sample rate is more than 2x the fundamental frequency and my output filter completely removes all bandwidth above the Nyquist frequency.  In reality, of course, it is easier to use a higher sample rate because the output filters can be made more easily.

Yes, if you want to produce only clean sine wave, then this true. You're just needs to take into account that filter is just attenuates unwanted components, it doesn't removes it. Also analog filter has smooth slope. So, you're needs to keep this slope inside first Nyquist zone.

Second, the fact that the sample rate is not a multiple or factor of the frequency is completely irrelevant.  It can be ANY NUMBER more than 2X. A sample rate that is not related to the frequency is NOT jitter.  All I have to do is accurately solve the equation f(x) = (amplitude * sin (frequency * 2 *pi *x)) with the appropriate constants for each sample point and my output will be perfect.

This generator produces not only sine wave, but also square wave, so you cannot say that half sample rate is good enough to PERFECTLY reproduce a square wave.

When your sample rate is not integer factor of target frequency, all harmonics of square wave which is outside first Nyquist zone will be spread around (you can see it as a grass on your 9.8 MHz FFT). When your sample rate is integer factor of square wave frequency, all harmonics of square wave will fit each other (you can also see it as missing grass on your 10 MHz FFT). So, there is no need infinite sample rate to perfectly reproduce square wave, you can do it with sample rate which is integer factor of target frequency and first harmonic of square wave fits to first Nyquist zone :)

This is why "the fact that the sample rate is not a multiple or factor of the frequency" is a relevant issue here  :)

The second issue here is that you're needs to synthesize required frequency for DAC sample rate. The problem here is that if sample rate is not integer factor of target frequency, your NCO will have jitter. The best you can do is to minimize it's effect. But in reality usual NCO has bad spurious performance due to different software limitations. So, the jitter will be there :)

And this is why it is also relevant for sine wave. :)


Third, even your assertion that you can't get a perfect sine wave from a clock with jitter is wrong, although in practice it would generally be true.  If you apply a technique used in Equivalent Time Sampling on some DSOs, you can have the samples at a more or less random rate (as long as it always exceeds Nyquist) as long as you are able to accurately measure the exact timing of the sample and apply the calculation to that time.

Equivalent Time Sampling cannot improve jitter performance. Even more ETS doesn't uses fixed sample rate. It uses sample rate with very small phase shift for every sampling cycle interval. Very interesting - how you're imagine the same approach for single DAC?  :)

« Last Edit: July 14, 2019, 03:26:51 am by radiolistener »
 

Offline pantelei4

  • Regular Contributor
  • *
  • Posts: 90
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #60 on: July 14, 2019, 07:01:19 am »
I don't have it, I planned to buy it, but later changed my decision because of this issue with jitter which is reported by other users. I thought this is just DAC aperture jitter. But pantelei4 shows that there is much worse issue with jitter.
I had all the budget models of DDS - MHS, JDS, FY. The square wave jitter is not on the JDS6600, only on the duty cycle 50%.
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #61 on: July 14, 2019, 08:16:49 am »
what sample rate is used for DAC in FY6600?
 

Offline pantelei4

  • Regular Contributor
  • *
  • Posts: 90
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #62 on: July 14, 2019, 08:23:17 am »
what sample rate is used for DAC in FY6600?
250MSa
« Last Edit: July 14, 2019, 08:31:37 am by pantelei4 »
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #63 on: July 14, 2019, 08:43:25 am »
250MSa

OMG  :o 

DAC904 is 165 MHz according to datasheet, so it is very overclocked  :D

Just tried to simulate square wave with NCO:
DAC sample rate: 250 MHz
NCO accumulator: 32 bits
FFT size: 256k  (selected to be more close to parameters from bdunham7 screens)
FFT window: Blackman Harris 4

And result looks pretty close to these FFT from bdunham7.


So, almost all these spurs are result of jitter :)
« Last Edit: July 14, 2019, 08:52:39 am by radiolistener »
 

Online FransW

  • Regular Contributor
  • *
  • Posts: 100
  • Country: nl
Re: Fy6800 vs Fy6900
« Reply #64 on: July 14, 2019, 12:41:46 pm »
Quote from: bdunham7 on Today at 06:21:51 am
First, we should define jitter, which could involve the generator sample clock, the scope/FFT trigger gate or the DDS process itself.

Check https://en.wikipedia.org/wiki/Jitter
for some aspects & definition.

Regards, Frans
« Last Edit: July 14, 2019, 12:44:49 pm by FransW »
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #65 on: July 14, 2019, 12:53:01 pm »
250MSa

OMG  :o 

DAC904 is 165 MHz according to datasheet, so it is very overclocked  :D


 Welcome to the Feeltech related fora, radiolistener  :)

 We've known this for some time (18 months or longer - ICBA to check out the early postings in the "FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator" thread which will be celebrating its 2nd anniversary on the 28th).

[EDIT] I started re-reading the FY6600 thread from the beginning (again! for the third time) and came across the relevant post (dated 4th Nov 2017) on the fourth page which had identified the DAC chip actually used (a finding that has never subsequently been over-turned).

https://www.eevblog.com/forum/testgear/feeltech-fy6600-60mhz-2-ch-vco-function-arbitrary-waveform-signal-generator/msg1340574/#msg1340574

 Old news indeed! ;)

 This overclocking will, no doubt, aggravate the random jitter noise (pico seconds) on sine waves and cousins but has little to do with the 4ns jitter issue with square waves and its cousins.

 I'm sure Feeltech must have checked out the over-clockability of these devices before going to the additional trouble of scrubbing the part numbers off. Maximum clock speed ratings on chips was (and to a slightly lesser extent still is) far from an exact science in their manufacture so the speed ratings tend to be rather conservatively specified on what speed capability is actually achieved in their production.

 It's not unusual for the actual speeds to be double what the specifications say they are. Once the production processes have been fine tuned to allow the manufacturers to offer even higher speed options at a premium, they eventually reach a stage in their production when they they can no longer meet demand for the cheaper, lower speed part by using actual lower speed parts so land up having to mark say a 320MHz part as a 165MHz part in order to shift their product and still retain the extra profit on the parts with the higher marked speed (low and high performance parts all costing the same to manufacture anyway - there weren't, and aren't, separate production lines for 165 and 320MHz wafers, they are simply tested and selected from each wafer's yield).

 This is a long established practice in the silicon chip manufacturing industry. Carry on serving the low end market demand by mislabelling the high speed parts to maintain sales even when you've gotten so good at making the premium priced parts that you no longer produce the low rated parts in any meaningful quantity and still collect from those customers prepared to pay the premium price in order to get a product that's guaranteed to meet their more stringent requirements. It's not dishonest exactly, it's more a case of putting the burden of select by testing on their cheaper customers' shoulders.

 Feeltech, like any good 'manufacturer of cheap electronic goods' know this and will test and select ICs  individually or in batches, leaving the rare exceptions to be discovered in the later product QA testing phase.

 If they've any sense, they'll test a 165MHz marked part they're planning on using at 250MHz by running it at 300MHz and at an elevated temperature such as 60 to 80 deg C (the innards of the FY6600 could reach 50 deg C on average with some parts reaching 70 deg C with the lid off). If you're going to risk a high returns rate on such a gamble, you'll be looking to make sure there's still a reasonable safety margin in such an 'overclocking' exercise on a significant and critical component. In short, the overclocking of that 165MHz part to 250MHz, is unlikely to be the issue it appears to be. ;D

  Obviously, there's still a risk of the customer receiving a unit where the DACs are right on the edge. If you think you may have been sold such a dud, I guess a simple way to check would be to monitor a square wave at exactly 10MHz where this 4ns jitter is theoretically absent, using a DSO with infinite persistence turned on to look for evidence of rogue 4ns jitter.

 For added 'credit' repeat the test with a nice insulating blanket draped over the generator to raise the temperature to increase the thermal speed reducing stress on the DAC (and everything else around it) even further. Inserting a thermal sensor probe into the case, whilst a sensible precaution, is optional (although knowing the actual temperature rise would be a useful data point :) ).

JBG
« Last Edit: July 15, 2019, 06:45:41 pm by Johnny B Good »
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #66 on: July 14, 2019, 02:58:50 pm »
Here is a new simulation with better resolution for DAC square wave output at 250 MHz for 10 MHz and 9.8 MHz with 32 bit NCO and no interpolation (just switch between max and min value).

It seems that the simulation result is almost identical with FFT measurements from bdunham7.

So, FY6600 definitely doesn't use interpolation for square wave.
Just simple NCO with 32 bit accumulator and simple min/max switch.  :)
 
The following users thanked this post: maxwell3e10

Offline bdunham7

  • Frequent Contributor
  • **
  • Posts: 330
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #67 on: July 14, 2019, 05:26:33 pm »
Can you run the same simulation with 9.8 and 10.0 MHz sine waves?
 
The following users thanked this post: Johnny B Good

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #68 on: July 14, 2019, 06:39:40 pm »
Here is a new simulation with better resolution for DAC square wave output at 250 MHz for 10 MHz and 9.8 MHz with 32 bit NCO and no interpolation (just switch between max and min value).

It seems that the simulation result is almost identical with FFT measurements from bdunham7.

So, FY6600 definitely doesn't use interpolation for square wave.
Just simple NCO with 32 bit accumulator and simple min/max switch.  :)

 Interesting. Those spectra show the expected odd harmonic peaks for a square wave. It's the in between peaks which are the undesired spurii.

 The TLA "NCO" had a familiar ring to it but I had to go searching to refresh my memory (so many acronyms, so little time).

 On a hunch I looked for a wikipedia article on DDS technology and found the NCO reference there which mentioned a link to their "Arbitrary waveform generator" article which neatly explains why we see the DAC clock jitter on square waves and other waves containing similar instantaneous transients but not on sine curved waves or triangles.

 The only puzzling thing being the apparent high speed rise and fall times on square waves that are being passed through an anti-aliasing(reconstruction) filter with an LPF cut off frequency somewhere between 75 and 100MHz (both comfortably below the Nyquist frequency of a DAC running at a sampling rate of 250Msps).

 I'm considering the possibility of the LPF cut off frequency being as high as 100MHz due to my seeing rise and fall times in the region of 3.8ns on a 200MHz BW scope with its own 1.8ns rise/fall time specification when viewing the Sinc-Pulse waveform at 10MHz.

 Strangely, the square wave shows its usual 7.2nS rise/fall times which can be pushed to 4.5ns when modulating CH1 with an identical square wave from CH2. It seems the square waves aren't going quite as fast as they possibly can, yet still produce a 4ns sampling clock jitter. ::)

[EDIT] I just tracked down the reference to this modulation trick

https://www.eevblog.com/forum/testgear/feeltech-fy6600-60mhz-2-ch-vco-function-arbitrary-waveform-signal-generator/msg1339581/#msg1339581

 Re-reading it, the comments regarding every other relative of the square wave having 4.4ns edges is rather interesting. I wonder if the doubling up of the square wave's rise/fall times were a failed attempt on Feeltech's part to mask the 4ns clock jitter issue. :-//

 For further amusement, I increased the frequency by 10mHz on both channels to see what effect, if any, such modulation would have on the strobed 4ns clock jitter and saw no change, just the speed boost on the rise/fall times from 7.2 to 4.5ns. Trying this modulation of CH1 with CH2 trick using the Sinc-Pulse doesn't speed the transition times, only slow them down a little.

 If you're looking to get the fastest possible rise/fall time pulse out of these function generators (and free of the DAC clock jitter to boot!), the Sinc-Pulse is definitely the clear winner (at least up to around a repetition rate of 20MHz or so - it starts getting messy much beyond that point).

JBG

PS

 After trawling through more pages of the FY6600 thread, I came across this interesting titbit by Fremen67 back in February last year where he mentions that square waves etc are treated differently to the arb waveforms which confirms the conclusions over which waveforms suffer from the 4ns jitter and which don't. You need to read the linked posting to get the idea as to just what was going on in regard of reviving the FY6600s that had been bricked by the earlier version 3.0 firmware.

https://www.eevblog.com/forum/testgear/feeltech-fy6600-60mhz-2-ch-vco-function-arbitrary-waveform-signal-generator/msg1426803/#msg1426803

 Re-reading the efforts being made to overcome Feeltech's utter contempt for those customers who had paid the price for their programming incompetence, impressed me by the sheer doggedness of Fremen67 and others in creating a solution that would not only overcome the issue of closed proprietary firmware that precluded any means of applying firmware updates but also offer a superior open source less Chinese user interface (specifically, their hallmark bad choice of font) which would support firmware updates/hacks to allow owners of the lower/cheaper spec 15, 20, 30 and 50 MHz models to upgrade to the 60MHz spec.

 Sadly, Fremen67 disappeared in the middle of all this development effort, never to be heard from again (with some fearing the worst for his unexplained disappearance), and the project lost its momentum and ground to a halt despite the promise of being able to hand Feeltech's ass back to them on a plate.

 The subsequent factory applied firmware updates on the later production remained free of any further fatal flaws relegating the original issue a matter of ancient history for myself and others who had been late to this particular party which sealed the fate of this open source firmware development effort.

 From then on, it was back to the interrupted business as usual of the more practical hardware based improvement modification projects, mostly based on refinements to the earlier modifications that had previously been described. As some members here know full well, that two year old thread is still very active.;)
« Last Edit: July 15, 2019, 12:41:54 am by Johnny B Good »
 

Offline bdunham7

  • Frequent Contributor
  • **
  • Posts: 330
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #69 on: July 14, 2019, 08:52:21 pm »
Quote from: bdunham7 on Today at 06:21:51 am
First, we should define jitter, which could involve the generator sample clock, the scope/FFT trigger gate or the DDS process itself.

Check https://en.wikipedia.org/wiki/Jitter
for some aspects & definition.

Regards, Frans

I guess I didn't say that very well.  By 'define jitter' I didn't mean jitter as a general concept--I think we can just assume that we are all talking about periodic jitter here as that is pretty standard and in any case periodic jitter is what my scope measures directly.

What I'm getting at is that you can't simply state that a particular signal has a certain amount of jitter, you need to define the points at which you measure that define the period. I'm not talking about tracing the jitter back to its source, just examining the signal as it is.  If you have a device that is triggered by the rising edge of a clock signal, it makes sense to define the period as the time between zero crossings of the rising edge and jitter as the variation from period to period.  You can pick a different place to measure as long as you say what it is.  Failing to agree on this can result in vastly different results and I've come up with an example.

I'm imagining a system where you have an ADC used for audio recording at 192KSa/s and the sample-and-hold circuit is clocked to this signal, triggered on the rising edge.  I've set up a signal generator to produce a 192KHz square wave but with the duty cycle modulated by noise with a maximum deviation of 20%.  This is the first picture and you can see that the falling edge varies but the critical rising edge is stable and shows a few hundred picoseconds jitter.  Not great but good enough.  The next picture is an FFT of that signal and it shows a 192KHz signal with a lot of noise.  Without the modulation, the noise floor would be off the bottom of the screen.

785061-0

785055-1

So now we take the signal and simply invert it.  I did this by reversing the polarity of the signal generator, not the scope. The rising and falling edges swap places and now you have a very jittery signal, totally unacceptable for the purpose I stated.   However, if I change the trigger on the scope to the falling edge, it goes right back to the lower jitter number.  And, as expected, an FFT of the inverted signal is exactly the same.

785049-2

785043-3

785037-4

This should all seem obvious, but maybe it isn't.  You can't look at an FFT of a signal and declare that it has a certain amount of jitter.  Jitter is not a single number that can be assigned to a signal without further qualification.  Equivalent jitter?  Some other term?  Maybe.  But here I've shown a simple example of a signal that may work very well as a low-jitter (or low-enough jitter) clock and yet shows huge noise on an FFT that is indistinguishable from jitter.  And the measured jitter varies by factor of 50 depending on what point you trigger at.
« Last Edit: July 14, 2019, 08:57:12 pm by bdunham7 »
 

Offline Adrian_Arg.

  • Regular Contributor
  • *
  • Posts: 249
  • Country: ar
Re: Fy6800 vs Fy6900
« Reply #70 on: July 15, 2019, 12:22:21 am »
hello, after thinking about it I changed my mind, I just bought a Kkmoon FY6900 60mHz, it was not worth saving dollars from a 30mHz to a 60mHz, on aliexpress.com, I hope it arrives in good condition. :popcorn:
« Last Edit: July 16, 2019, 01:31:43 am by Adrian_Arg. »
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #71 on: July 15, 2019, 07:33:33 pm »
hello, after thinking about it I changed my mind, I just bought a Kkmoon FY6800 60mHz, it was not worth saving dollars from a 30mHz to a 60mHz, on aliexpress.com, I hope it arrives in good condition. :popcorn:

 Considering just how lightweight these devices are (just 700 grammes - the box and packaging will likely weigh as much, if not more), even if they're drop shipped from an aircraft at 10,000 feet sans parachute, they're likely to arrive unharmed due to their very low terminal velocity. The box might look a bit bashed but the FY6800 inside might only need a ribbon cable connector or two at most to be reconnected/reseated. >:D

 Apropos of ribbon cable connectors, if the unit fails to function when you try it out for the first time, it's well worth opening it up (four long screws in the base and an old credit/debit card for a spudger to unclip the top of the front panel from the lid) to check these connections out. A few recipients have discovered loose connectors flapping around when investigating such post delivery failures, no doubt more than likely from errors in assembly which managed to slip past Feeltech's QA testing programme :-DD

JBG
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #72 on: July 16, 2019, 11:18:09 am »
Quote from: bdunham7 on Today at 06:21:51 am
First, we should define jitter, which could involve the generator sample clock, the scope/FFT trigger gate or the DDS process itself.

Check https://en.wikipedia.org/wiki/Jitter
for some aspects & definition.

Regards, Frans

I guess I didn't say that very well.  By 'define jitter' I didn't mean jitter as a general concept--I think we can just assume that we are all talking about periodic jitter here as that is pretty standard and in any case periodic jitter is what my scope measures directly.

What I'm getting at is that you can't simply state that a particular signal has a certain amount of jitter, you need to define the points at which you measure that define the period. I'm not talking about tracing the jitter back to its source, just examining the signal as it is.  If you have a device that is triggered by the rising edge of a clock signal, it makes sense to define the period as the time between zero crossings of the rising edge and jitter as the variation from period to period.  You can pick a different place to measure as long as you say what it is.  Failing to agree on this can result in vastly different results and I've come up with an example.

I'm imagining a system where you have an ADC used for audio recording at 192KSa/s and the sample-and-hold circuit is clocked to this signal, triggered on the rising edge.  I've set up a signal generator to produce a 192KHz square wave but with the duty cycle modulated by noise with a maximum deviation of 20%.  This is the first picture and you can see that the falling edge varies but the critical rising edge is stable and shows a few hundred picoseconds jitter.  Not great but good enough.  The next picture is an FFT of that signal and it shows a 192KHz signal with a lot of noise.  Without the modulation, the noise floor would be off the bottom of the screen.

(Attachment Link)

(Attachment Link)

So now we take the signal and simply invert it.  I did this by reversing the polarity of the signal generator, not the scope. The rising and falling edges swap places and now you have a very jittery signal, totally unacceptable for the purpose I stated.   However, if I change the trigger on the scope to the falling edge, it goes right back to the lower jitter number.  And, as expected, an FFT of the inverted signal is exactly the same.

(Attachment Link)

(Attachment Link)

(Attachment Link)

This should all seem obvious, but maybe it isn't.  You can't look at an FFT of a signal and declare that it has a certain amount of jitter.  Jitter is not a single number that can be assigned to a signal without further qualification.  Equivalent jitter?  Some other term?  Maybe.  But here I've shown a simple example of a signal that may work very well as a low-jitter (or low-enough jitter) clock and yet shows huge noise on an FFT that is indistinguishable from jitter.  And the measured jitter varies by factor of 50 depending on what point you trigger at.

 If you do the following experiment, you'll see that both edges of the square wave are equally effected by this 4ns DAC clock jitter (and also confirm that sinusoids are free of such defect).

 Set both channels to exactly 10MHz (one of the 'golden frequencies, devoid of the 4ns jitter on square waves) and then dial in a minus or plus 10mHz offset on each channel. Set one channel for square wave and the other for sine wave output and choose a convenient Vpp setting for both (5Vpp works just fine). Observe the outputs on a 'modern' dual channel 'scope with a bandwidth of at least 50MHz so as to show a reasonable facsimile of the 10MHz square wave and trigger from the sinusoidal waveform.

 What you'll see from this experiment is the reason why your FFT measurements show no difference between the apparent cases of this 4ns jitter only effecting either the leading or trailing edge of the square wave. The reason being that both edges are effected equally (even though alternately).

 Unless edge jitter is so severe as to prevent your 'scope's triggering circuit obtaining a stable trigger, the edge it is triggering from will always appear to be "jitter free" with  all of the jitter component of both edges accumulated onto the non-triggered edge.

 Keep in mind that in this case, the time period between rising edges and between falling edges will remain constant with this form of timing jitter simply switching the unequal duty cycle polarity at a rate which depends on the offset from the 'golden frequency'. Using in this case, a 10mHz offset allows us to observe in slow motion exactly what happens at the more typical KHz offsets from the 'golden frequency' where it all becomes a blur.

 If you so desire, you can report your results and perhaps even thank me. ;)

JBG
 
 

Offline bdunham7

  • Frequent Contributor
  • **
  • Posts: 330
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #73 on: July 16, 2019, 07:33:49 pm »
@JBG

I think we're talking of two different things.  My demonstration has nothing to do with the 4ns issue and wasn't even done on a Feeltech sig gen.  I'm demonstrating that you you can have two clock signals, one with no measured jitter (assuming a particular measurement point--in this case the rising edge) and one with a lot and both can have identical FFTs.

You should go one step further with your demo and see what the calculated RMS jitter is, if you have the feature.  You'll be suprised at how low this can be even when the deviations are due to the 4ns effect.  And try using 5 MHz as your 'magic' frequency because it is at 5 MHz that the FY6600 is truly free of the 4ns effect, as both period and duty cycle are times perfectly.
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #74 on: July 17, 2019, 01:16:47 pm »
@JBG

I think we're talking of two different things.  My demonstration has nothing to do with the 4ns issue and wasn't even done on a Feeltech sig gen.  I'm demonstrating that you you can have two clock signals, one with no measured jitter (assuming a particular measurement point--in this case the rising edge) and one with a lot and both can have identical FFTs.

You should go one step further with your demo and see what the calculated RMS jitter is, if you have the feature.  You'll be suprised at how low this can be even when the deviations are due to the 4ns effect.  And try using 5 MHz as your 'magic' frequency because it is at 5 MHz that the FY6600 is truly free of the 4ns effect, as both period and duty cycle are times perfectly.

 Thanks for that suggestion bdunham7, I'll run the experiment later and let you know the result.

 I'm on your side in this argument that radiolistener has put forward about this 4ns jitter being present on all of the waveforms - it isn't.

 Obviously, all waveforms will exhibit some level of jitter but it won't necessarily be of the 4ns DAC clock period kind we see quite clearly on square waves and related waveforms when not being generated at their 'Golden Frequencies' of, in this case, our dearly beloved FY6600 and its progeny.

 Indeed, one could be forgiven for thinking the jitter noise, such as it is in the sine waveform output when observed with a DSO, is nothing more than the effect of analogue noise present in the output of any analogue oscillator from Colpitts to Wien Bridge.

 Before I ran this test, I'd thought the suggestion to use a Schmidt triggered input gate with the sine wave output to generate a square wave at any frequency, sanitised of this 4ns clock jitter, may magically resurrect this clock jitter in a demonstration of "Sod's Law". Thankfully, it seems this trick is beyond the "Law", including that of Sod. >:D

 This "Use a clipped sine wave" trick had just seemed too easy to be true. Of course, whilst that's good for producing a 'jitter free' square wave, it still presents additional complexity[1] when other than 50% ratio square waves and one shot pulses are required (but let's just deal with one problem at a time,  ;)).

[1] Ranging from dc coupling into our external squaring box of tricks and varying the dc offset, to ac or dc coupling the sine wave into a more complex box of tricks with its own independent controls over duty cycle and 'one shottedness' (manual trigger or a programmable repetition rate or WHY), along with Vpp level settings.

JBG
« Last Edit: July 17, 2019, 01:20:01 pm by Johnny B Good »
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #75 on: July 17, 2019, 04:48:13 pm »
Before I ran this test, I'd thought the suggestion to use a Schmidt triggered input gate with the sine wave output to generate a square wave at any frequency, sanitised of this 4ns clock jitter, may magically resurrect this clock jitter in a demonstration of "Sod's Law".

It will be surprise for you to find "missing" jitter after trigger, but this is not magic, that's normal behavior...  ;D
This jitter didn't resurrected, it is already present in the sine wave. But you just didn't notice it due to slow slope :)

« Last Edit: July 17, 2019, 05:00:21 pm by radiolistener »
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #76 on: July 17, 2019, 04:54:09 pm »
So now we take the signal and simply invert it.  I did this by reversing the polarity of the signal generator, not the scope. The rising and falling edges swap places and now you have a very jittery signal, totally unacceptable for the purpose I stated.   However, if I change the trigger on the scope to the falling edge, it goes right back to the lower jitter number.  And, as expected, an FFT of the inverted signal is exactly the same.

it doesn't matter what polarity you select, the jitter is the same. This is how oscillscope trigger works. It shifting waveform in such way, so the trigger point will be at the center of display. And this is why you don't see jitter edge at the center. It still jittering, but oscilloscope shifting waveform in such way so you're don't see it. :)
« Last Edit: July 17, 2019, 06:13:04 pm by radiolistener »
 

Offline bdunham7

  • Frequent Contributor
  • **
  • Posts: 330
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #77 on: July 18, 2019, 12:34:07 am »
So now we take the signal and simply invert it.  I did this by reversing the polarity of the signal generator, not the scope. The rising and falling edges swap places and now you have a very jittery signal, totally unacceptable for the purpose I stated.   However, if I change the trigger on the scope to the falling edge, it goes right back to the lower jitter number.  And, as expected, an FFT of the inverted signal is exactly the same.

it doesn't matter what polarity you select, the jitter is the same. This is how oscillscope trigger works. It shifting waveform in such way, so the trigger point will be at the center of display. And this is why you don't see jitter edge at the center. It still jittering, but oscilloscope shifting waveform in such way so you're don't see it. :)

I know how the trigger works.  I'm referring to the first rising edge after the trigger (the last picture). And my scope doesn't agree with you that the jitter is the same.  Why is that?
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #78 on: July 18, 2019, 01:34:50 am »
Before I ran this test, I'd thought the suggestion to use a Schmidt triggered input gate with the sine wave output to generate a square wave at any frequency, sanitised of this 4ns clock jitter, may magically resurrect this clock jitter in a demonstration of "Sod's Law".

It will be surprise for you to find "missing" jitter after trigger, but this is not magic, that's normal behavior...  ;D
This jitter didn't resurrected, it is already present in the sine wave. But you just didn't notice it due to slow slope :)

 It wasn't any surprise to discover that the theory worked in practice. I can't understand why you keep insisting that this 4ns clock jitter exists in the sinusoidal waveforms when it plainly does not. This 4ns jitter isn't hidden by the "slow slope" as you put it because it was never there in the first place!  ::)

 I've just run some tests using the 5MHz square wave as suggested by bdunham7. This is free of the 4ns jitter everyone seems to be obsessed with in this cheap signal generator. Furthermore, unlike the 10MHz square wave, it has a perfect 50% duty cycle.

 Using this as my trigger source, I see only the 2 or 3 hundred peak to peak picoseconds of noise jitter on sine wave and Sinc-Pulse when zoomed in at 1ns per division and the Y amplifier gain set to 20mV per division (some 26dB in excess of that required to show the full 5Vpp sine wave (2.5Vpp into the 50R dummy load) on the display so as to zoom in on the zero crossing region to increase visibility of this jitter noise). I can't use this much excess gain with the Sinc-Pulse without this making the jitter look worse but the steep flanks don't require as much gain to show the jitter noise anyway.

 If I offset the sine wave frequency by +/-10mHz, I see a steady drift against the square wave trace from which I'm triggering the 'scope. If I trigger from the sine wave (or Sinc-Pulse) set exactly on 5MHz and offset the square wave by 10mHz instead, I see it drift in discrete 4ns steps with both edges in unison, unlike the 10MHz case where each edge alternately jumped 4ns at a time giving the frequency drift a shuffling effect (this confirms the 50% duty cycle of the 5MHz square wave, btw).

 If the divisor used to generate the frequency from a 250MHz clock isn't an exact even integer as for the 10MHz case (25) you get this asymmetric effect on the duty cycle. The 5 and 25MHz settings both produce a perfectly symmetric square wave (divisor values of 50 and 10 respectively - both even integers). It works with all even integers from 6 upwards (4 corresponds to 62.5MHz so can't be used in this case). The 6 divisor corresponds to 41.666666666667MHz, an irrational number. The 8 divisor -> 31.25MHz a nice easy number to dial in. 10 we know already, 12 -> 20.833333333333MHz, another irrational number, and so on.

 The "Take away" from all this is that sinusoids are immune to the 4ns 'jitter' that afflicts square waves and can be used to drive a Schmitt triggered high speed logic gate to generate square waves free of this 4ns jitter issue after all. :)

JBG
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #79 on: July 18, 2019, 04:19:12 am »
I'm referring to the first rising edge after the trigger (the last picture). And my scope doesn't agree with you that the jitter is the same.  Why is that?

I think this is because the first picture is taken for 192.00 kHz and the second picture is taken for 192.10 kHz   :)
You can find it in Freq Mean column of oscilloscope statistic measurements  ;)
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #80 on: July 18, 2019, 04:28:29 am »
The "Take away" from all this is that sinusoids are immune to the 4ns 'jitter' that afflicts square waves and can be used to drive a Schmitt triggered high speed logic gate to generate square waves free of this 4ns jitter issue after all. :)

sine waveforms are not immune to jitter. But you're may be right. This 4 ns jitter may appears because square wave is generated with no interpolation. While sine wave cannot work without interpolation, so it definitely uses some interpolation. And this is may be the reason why square wave has much higher jitter than sine wave. But sine wave also has some jitter.

It needs to be tested with high speed digital level buffer which has good enough rise time, for example 1 ns or better.
 

Offline bdunham7

  • Frequent Contributor
  • **
  • Posts: 330
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #81 on: July 18, 2019, 04:35:36 am »
I'm referring to the first rising edge after the trigger (the last picture). And my scope doesn't agree with you that the jitter is the same.  Why is that?

I think this is because the first picture is taken for 192.00 kHz and the second picture is taken for 192.10 kHz   :)
You can find it in Freq Mean column of oscilloscope statistic measurements  ;)

That accounts for the measured jitter being 40 times as high as the same signal measured differently?  :palm:  It's the exact same signal as the second display.  The the way the scope measures frequency keeps it from being very accurate under the conditions displayed.
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #82 on: July 18, 2019, 05:53:19 am »
That accounts for the measured jitter being 40 times as high as the same signal measured differently?  :palm:  It's the exact same signal as the second display. 

That's not the same signal, previously you're wrote:

I did this by reversing the polarity of the signal generator, not the scope.

You're changed parameter of signal generator and now you're talking that this is exact the same signal... We cannot assume that this is the same signal, because we don't know what is going on inside signal generator when you change this parameter.

There are several possible issues for that, for example:
1) signal generator bug, for inverted polarity it may produce a little different frequency
2) your're randomly changed frequency for a little (when applied inverted polarity parameter)

We can see 192.10 kHz average frequency on the second screen, while it was 192.00 kHz on the first one  ;)

So, this is NOT exact same signal :)
And different jitter behavior also confirms that these signals are different.
« Last Edit: July 18, 2019, 06:09:01 am by radiolistener »
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #83 on: July 18, 2019, 06:40:42 am »
If the divisor used to generate the frequency from a 250MHz clock isn't an exact even integer as for the 10MHz case (25) you get this asymmetric effect on the duty cycle.

asymmetric effect appears here due to bad sample rate to signal freqeuncy relation.

10 MHz wave has 100 ns period. In order to reproduce it with no asymmetric issue, you're needs to generate edges with 100 ns / 2 = 50 ns period.

FY6800 uses 250 MHz sample rate, this is 4 ns step. So it cannot reproduce edges for time period which is not integer multiple of 4 ns.

50 ns is not integer multiply of 4 ns, because 50 ns / 4 ns = 12.5. This is why you cannot generate 10 MHz at 250 MHz sample rate with no distortion.

These distortions is visible on the spectrum as even harmonics (20 MHz, 40 MHz, 60 MHz,...).

This effect can be solved by change DAC sample rate in such way so it will be able to reproduce edges of the signal with no time error. For example, you can use DAC sample rate 200 MHz, in such case it will be able to reproduce edges with 50 ns period, your 10 MHz square wave will be clean with no even harmonics.
« Last Edit: July 18, 2019, 06:50:15 am by radiolistener »
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #84 on: July 18, 2019, 07:14:16 am »
Can you run the same simulation with 9.8 and 10.0 MHz sine waves?

In order to run it for sine wave there is needs to know what kind of NCO they are using in FY6600. It can be implemented with different precision/complexity, and it leads to different spurious performance.

I don't have information how it is implemented in FY6600.
 

Offline bdunham7

  • Frequent Contributor
  • **
  • Posts: 330
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #85 on: July 18, 2019, 04:06:47 pm »
There are three pictures of signals.  The first was not inverted, the second was inverted with the trigger set for falling edge, the third was  inverted with a rising edge trigger.  So the second and third are the same signal, but the measured jitter varies by a factor of 40.  I've stated all that clearly more than once.  The frequency "difference" you've latched onto is just nothing---the signal has not actually changed.
« Last Edit: July 18, 2019, 04:15:46 pm by bdunham7 »
 

Offline bdunham7

  • Frequent Contributor
  • **
  • Posts: 330
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #86 on: July 18, 2019, 04:11:51 pm »
I  think it pays to be a little more hard-hearted with sellers.  You have 30 days from the last delivery date to file INR, and some of these guys will say anything to try and run the clock out.  This is seller honghong20, right?  I haven't received mine nor you yours, so I think it is possible that no packages have been sent.  Talk of refusing packages is pretty strange--you should NEVER refuse a package according to eBay--and the seller wouldn't want to incur the return shipping charges that would likely exceed the value of the transaction.

 Thanks for that worrying advice (I think :-//).

 I've only ever communicated via Ebay's INR Request system which advised me to try and resolve a solution with the trader and telling me I could raise the issue on the 19th if not resolved to my satisfaction by then.

 I've seen mentions of delaying tactics being used by some Ebay traders so I am mindful of the issue. In this case, we're dealing with different traders (although possibly the same under two different names). I'm dealing with a trader with the name of "hgfurniture2018",  "Based in China, hgfurniture2018 has been an eBay member since 09 Jun, 2018", so just over a year in business. His feedback score is 4608 with a 98.6% positive Feedback rating.

 I know that feedback ratings generally need to be larger than 99.8% to instil full confidence and I'm not sure whether a 13 month trading history is long enough to reduce the risk of a fly by night disappearing act being pulled - is it long enough?

 Do Ebay monitor these negotiations or do you have to explicitly describe them when seeking their assistance? The email from Ebay suggests they're aware of the content of these communications so, maybe they do record them for 'posterity' to help resolve any disputes. :-// If Ebay advise against refusing a delivery, that request should raise alarms if not an eyebrow or two.

 I've replied to their suggested remedy with caveats of my own so I'm now awaiting their response before I query with Ebay their request that I refuse a second package turning up after they've sent a replacement to see if this is an acceptable action in this circumstance.

JBG

Well, it looks like I'm not getting my bargain FY6600s after all.  I asked the seller for a tracking number and he replied:

Dear buyer,
sorry for the trouble that carrier informed us that your packages was lost on the way,
we can offer you refund,
please tell us and we can arrange it asap.
Sorry for the inconvenience .


Now he'll offer me a refund thru Paypal (that I'll have to pay fees on but I won't know that until too late) and then maybe he'll claw the money back from Paypal 3 months from now.  Or it is possible he is just wriggling out of a loss from a mistaken listing by refusing to ship.  Either way, a huge waste of my time.  And look at the feedback!

Oh well, I guess I should be glad eBay is in the middle.
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #87 on: July 18, 2019, 06:51:27 pm »
Can you run the same simulation with 9.8 and 10.0 MHz sine waves?

In order to run it for sine wave there is needs to know what kind of NCO they are using in FY6600. It can be implemented with different precision/complexity, and it leads to different spurious performance.

I don't have information how it is implemented in FY6600.

 No one does. It's a black box with closed source encryption protected firmware in its front panel controller driving an fpga that does the donkey work in ways we can only speculate on. We can make educated guesses from published articles on various DDS technologies but there's no easy way to establish the actual details of Feeltech's implementation in their FY6*** series of function generators.

 At just 80 dollars or so,  it doesn't take too much imagination as to how Feeltech implemented their solution to masking this 4ns jitter issue with square and pulse waveforms. I'm guessing they took a pragmatic approach, allowing the 4ns jitter rather than use a more complex solution to compromise rise and fall times as seems to be the way Siglent have done this in their later low jitter models.

 It helps that their choice of unusually high sampling rate would hold this down to a mere 4ns versus the more typical 8ns or worse of the earlier models of expensive DDS signal generators. However, the 7.2ns rise and fall times on square waves (but not on its close cousins possessed of "infinitely fast" peak to peak transitions), suggests Feeltech had deliberately endowed its edges with additional 'slope' in the hope that it would mitigate this issue.

 Unfortunately for Feeltech, if the unusually slow transition times of 7.2ns versus the 3.8ns that can be achieved with a 250Msps sampling rate was the result of such a deliberate design choice, it hasn't done any good. The jitter is still present despite the enforced slower rise and fall times. It seems they may have compromised the square waveform for zero gain. Presumably Feeltech's designer had felt so confident that this "No Brainer" trick would work, he simply neglected testing that it would actually be of benefit.

 Getting back on topic, the square wave output from an FY6900 just might possibly now have faster 3.8ns transition times. ::) Anyone reviewing this latest offering from Feeltech should take particular interest in these two zero cost enhancements, the restoration of 3.8ns edges on the square wave output and the reworking of the 86R 20ishdB attenuator that's switched into circuit for voltage settings below half a volt p-p,  into one with a 50R impedance.

JBG
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #88 on: July 18, 2019, 07:52:28 pm »
At just 80 dollars or so,  it doesn't take too much imagination as to how Feeltech implemented their solution to masking this 4ns jitter issue with square and pulse waveforms. I'm guessing they took a pragmatic approach, allowing the 4ns jitter rather than use a more complex solution to compromise rise and fall times as seems to be the way Siglent have done this in their later low jitter models.

I'm agree, it has pretty good performance. It seems that it prety close to the best quality for fixed sample rate DAC. May be there is possible improvement for sine wave NCO, but I don't think such improvement will be significant. So, it does it's job very well... for fixed sample rate DAC of course... :)

But it can do it better with variable sample rate  ^-^
« Last Edit: July 18, 2019, 07:57:07 pm by radiolistener »
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #89 on: July 18, 2019, 08:08:21 pm »

Well, it looks like I'm not getting my bargain FY6600s after all.  I asked the seller for a tracking number and he replied:

Dear buyer,
sorry for the trouble that carrier informed us that your packages was lost on the way,
we can offer you refund,
please tell us and we can arrange it asap.
Sorry for the inconvenience .


Now he'll offer me a refund thru Paypal (that I'll have to pay fees on but I won't know that until too late) and then maybe he'll claw the money back from Paypal 3 months from now.  Or it is possible he is just wriggling out of a loss from a mistaken listing by refusing to ship.  Either way, a huge waste of my time.  And look at the feedback!

Oh well, I guess I should be glad eBay is in the middle.

 I'm sorry to hear that. Whilst the exchange of correspondence between hgfurniture2018 and myself during this past week has finally resulted in a second shipment now in the process of being made, the chinglishisms do hint vaguely at the possibility of this being a much better thought out scam than yours, so I may also ultimately suffer the same fate - non delivery and a refund.

 After being assured the FY6600-60M they were going to send me was of new stock and my request that they at least provide estimated dates for its delivery in my penultimate message, they responded with this:-

"'dear customer, sorry for the problem . It may need 10-15 days to wait another one .Is it fine ? best wishes"

to which I replied:-

"Dear Sir, Ten to fifteen days delivery time is acceptable. You may proceed with the shipment. Regards"

 This elicited the following reply:-

"dear customer, We have arranged to send you a new one. Everything would be fine.please wait patiently. Please don’t worry. Any question later, please kindly come back to me firstly, i will try my best to help you solve it well. Best wishes and have a nice day! Best wishes"

 In their original reply, they had offered me the options of sending another generator or provide a refund. Ever since then, the conversation was all about meeting my caveats and verifying the address details they had before sending the replacement out. If it is a ruse to avoid selling an item they could otherwise charge double for, the address verification request was rather a nice touch. ::)

 I'll not be closing the request until it's either delivered or I've given up and requested a full refund. The incident won't be closed until I have that sig genny in my grubby mitts or else a full refund into my account. It's possible I might effectively land up in your situation, only another 3 or 4 weeks down the line.

 Now all I can do is sit tight and wait in the hope that Ebay's involvement will force them to keep their promises. Luckily, it's not a "Life or Death" matter, just a waste of time with only a refund for consolation should the worst come to the worst. It's just that it would be rather nice to have an unmodified 'spare' to play around with to compare with the original unit I've upgraded "beyond all recognition".

 Ah well, only another 10 to 15 days to go, according to the seller. :-//

JBG

 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #90 on: July 18, 2019, 10:46:11 pm »
At just 80 dollars or so,  it doesn't take too much imagination as to how Feeltech implemented their solution to masking this 4ns jitter issue with square and pulse waveforms. I'm guessing they took a pragmatic approach, allowing the 4ns jitter rather than use a more complex solution to compromise rise and fall times as seems to be the way Siglent have done this in their later low jitter models.

I'm agree, it has pretty good performance. It seems that it prety close to the best quality for fixed sample rate DAC. May be there is possible improvement for sine wave NCO, but I don't think such improvement will be significant. So, it does it's job very well... for fixed sample rate DAC of course... :)

But it can do it better with variable sample rate  ^-^

 I've just been looking at the specifications for the Siglent SDG1062X Signal Generator as the most comparable to the FY6600 of the relatively inexpensive upmarket class of signal generator - a snip at only £440 compared the £75.66 I paid for mine (admittedly, I've spent some 40 to 50 quid on parts to upgrade it ::) ).

http://www.labtronix.co.uk/drupal/sites/default/files/sdg1000x/SDG1000X_DataSheet_DS0201X_E01A.pdf

 Prior to my purchasing the FY6600, I had been considering the cheaper 30MHz version, the SDG1032X for a mere £360 (just a fiver less than I'd paid for my SDS 1202X-E dual channel 200MHz BW DSO a week or two before). I got the impression that there was a large element of "Swings and Roundabouts" between the Siglent and the Feeltech generators so thought, in view of all the upgrading fun to be had, the best "Starter" option would be to go for the FY6600. A mistake at £75.66 is far easier to swallow than one costing £360 or £440. :)

 You have to start spending ten times the price of that FY6600 before you get a signal generator that shows no weaknesses compared to any of the Feeltech's best performance figures. For anyone with a fresh or renewed interest in electronics as a hobby, these Feeltech generators are an excellent starter choice - even its limitations are an education alone. ::)

 Anyway, I thought I'd try and record 30 second movie snippets of what happens when you configure a square wave on one channel with a sine wave on the other, both set to 20.833333333333MHz with first one offset by 30mHz with the other triggering the 'scope, then a reversal of which triggers the 'scope and which has its frequency offset.

 I recorded 320 by 240 30fps MOV files which I was able to compress below the 1MB limit using handbrake. The low resolution leaves a lot to be desired (like more resolution - but, what the hey! :) ) but is just sufficient to show how each waveform performs its 'drift' against a jitter free reference (20.833333333333MHz being one of those awkward 'golden' jitter free frequencies for our square wave output).

 Having discovered eeblog's limited choice of file extensions, I've stored them as zip files. Being already compressed, there's no point in asking any lossless compression algorithm to compress the uncompressible. ::)

 They're named to reflect the test. Whatever is reference always has its frequency set to the 'golden' one with the other being offset by 30mHz. The timebase is set to 5ns per division with both channels set to 500mV per division. The generator is set for a p-p of 5v both channels terminated with 50 ohms. TBH, I'm impressed that the square wave looks as square as it does at this frequency.  ;D

JBG

PS, the damned kakamaimee interface eevblog is using has screwed my attachment selection yet one more time so I've had to do a follow up post since there's no obvious way to retrieve the situation.
« Last Edit: July 19, 2019, 03:36:32 am by Johnny B Good »
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #91 on: July 18, 2019, 10:54:58 pm »
 Hopefully, this is the missing zip file. >:( >:( >:( :palm:

JBG

[Edit]  I see it worked this time.
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #92 on: July 19, 2019, 01:11:39 pm »
Johnny B Good, is it possible to calibrate FY6600 for real amplitude voltage?

I mean is it possible to calibrate it in such way, so I can set 1 Vpp, connect 50 Ohm load on the output and get real 1 Vpp. This is expected behavior and it is too complicated to convert voltage into some strange "Chinese volts" which is twice higher than standard volts.
 

Offline pantelei4

  • Regular Contributor
  • *
  • Posts: 90
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #93 on: July 19, 2019, 02:20:44 pm »
I mean is it possible to calibrate it in such way, so I can set 1 Vpp, connect 50 Ohm load on the output and get real 1 Vpp.
It has an output resistance of 50 ohms.
And the amplitude is set without load.
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #94 on: July 19, 2019, 04:28:56 pm »
Johnny B Good, is it possible to calibrate FY6600 for real amplitude voltage?

I mean is it possible to calibrate it in such way, so I can set 1 Vpp, connect 50 Ohm load on the output and get real 1 Vpp. This is expected behavior and it is too complicated to convert voltage into some strange "Chinese volts" which is twice higher than standard volts.

 I'm glad you asked me that question, radiolistener.  >:D  It gives me an excuse (and the opportunity to attach higher resolution movie files of the previous 'scope traces) to explain why this lack of accounting for high impedance versus matched impedance voltage levels when setting the output level is not the heinous crime many posters to this thread seem to think it is.

 I guess the Chinese didn't want to add that particular 'Bell' to the "Bells and Whistles" list. Not only that, they may have wanted to avoid any possible insult to our intelligence by suggesting that us 'westerners' aren't even in possession of the most rudimentary of mathematical skills (i.e. being unable to handle simple multiplication and division by two and optionally 1.4141414) ::)

 This halving of the output voltage when driving a correctly terminated cable (or just a terminating dummy load directly) from a generator with an output impedance matching said cable and dummy load, is expected behaviour. If you observe unexpected behaviour such as no to very little volt drop or much more than the expected 6.02dB drop, you know something is wrong when driving a circuit that supposedly has an impedance of 50R.

 Indeed, when it comes to having the generator output impedance match the load, it doesn't have to - the key thing being that the terminating impedance matches that of the connecting cable (transmission line). For instance you can use a generator with an impedance of 75 ohm to drive a 50 ohm line, allowing for the additional 1.94dB drop (a 60% drop versus the matched case of a 50% drop).

 In any case, the operator usually has to press a button to tell the signal generator that it should scale the p-p voltage setting to match the operating mode (matched or high impedance loading). The fancy and more expensive signal generators may well offer such a feature. Considering your question, they probably do and possibly by monitoring the current versus voltage output to calculate the actual impedance it is connected to so as to leave the operator a hand free to scratch their balls.

 Personally speaking, I'm rather glad that the Chinese designers of cheap affordable T&M kit have avoided this insult to the intelligence of their hobbyist target market demographic by not adding such unnecessary "Bells and Whistles" which would detract from the budget allowed for offering the  best possible performance at such a low price point. There's only so much money to go round and I'd rather it was all spent on the core features of my signal generator rather than diluted by such "inessentials".

 In this case, the voltage setting is based on the unloaded condition, leaving the operator to expect half this voltage if and when driving a matched load. This characteristic of your 'basic' signal generator is a very useful diagnostic aid in the hands of anyone familiar with basic transmission line theory, in particular the bit that says maximum power transfer between the generator and its load occurs when their impedances match each other as well as any transmission line linking the two.

 Calibrating the voltage setting for the unloaded condition is the most logical choice (it's very easy to check this well defined unloaded voltage output). It's also useful that it's calibrated this way since anyone working with audio frequency gear outside of communications equipment maintenance or design, will generally be driving high impedance loads, making the voltage setting immediately useful without the complication of having to divide by two or subtract 6dB. >:D

 In answer to your question... what was it again? Oh yes, the business of the unloaded voltage being a "Chinese Thing"(tm) and the possibility of having the voltage setting expressed as that which a matched load would produce (i.e. display 1Vpp instead of 2Vpp to account for the loading effect of a termination matching the output impedance of the generator).

 The answer in the case of these Feeltech generators is no (at least for the moment - if development of an OSS front panel firmware package ever resumes (seems rather unlikely though) you may well get the opportunity to add this feature to your "Wish List").

 However, in the case of other more expensive T&M kit there's nothing to stop designers from implementing the additional complexity to achieve this, and to varying degrees of sophistication, ranging from a simple press button to toggle between the two basic calibrations which match the two reference impedance conditions of either a matched or open circuit (Hi Z) loading (a feature that could trivially be added to these cheap Feeltech generators), to a more sophisticated monitoring of both output voltage and current to not only compensate for the loading but also to calculate the impedance of the attached load  for display to the operator (only stopping short of wiping said operator's arse, of course! ::) ).

 Anyway, that's my view of the matter. You're free to accept or reject this viewpoint; I don't really care, I've said my piece on the subject.

 I've (hopefully this time!) attached higher definition movie files of the traces I posted in my previous two postings mainly to reduce the pain of having to watch the effect at such an execrable resolution of just 320x240. Please enjoy!  ;)

JBG
« Last Edit: July 19, 2019, 07:28:55 pm by Johnny B Good »
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #95 on: July 19, 2019, 04:41:16 pm »
I mean is it possible to calibrate it in such way, so I can set 1 Vpp, connect 50 Ohm load on the output and get real 1 Vpp.
It has an output resistance of 50 ohms.
And the amplitude is set without load.

 That is so succinctly put!  :)

JBG
 

Offline CDaniel

  • Frequent Contributor
  • **
  • Posts: 316
  • Country: ro
Re: Fy6800 vs Fy6900
« Reply #96 on: July 19, 2019, 04:53:14 pm »
So the output is "known" by the microcontroller , nothing new ,  but a Siglent or a similar generator is actually measuring the output in some way if you load it down ?
About this you don't find anything in manuals .
 

Offline bdunham7

  • Frequent Contributor
  • **
  • Posts: 330
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #97 on: July 19, 2019, 05:00:58 pm »
So the output is "known" by the microcontroller , nothing new ,  but a Siglent or a similar generator is actually measuring the output in some way if you load it down ?
About this you don't find anything in manuals .

On my Siglent SDG2042X/2112X you "select" the load impedance and it displays the voltage, halved when 50R is selected, but nothing actually changes in the output and no measuring is done.  The only difference between it and the lowly Feeltech is that it calculates--estimates--the amplitude with a hypothetical 50R load. 
 

Offline maxwell3e10

  • Frequent Contributor
  • **
  • Posts: 471
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #98 on: July 19, 2019, 05:49:37 pm »
That is how all function generators work. They either assume a certain load or let you set the load resistance and adjust the displayed voltage.
 

Offline Jacon

  • Contributor
  • Posts: 32
  • Country: pl
Re: Fy6800 vs Fy6900
« Reply #99 on: July 19, 2019, 06:18:20 pm »
I've (hopefully this time!) attached higher definition movie files of the traces I posted in my previous two postings mainly to reduce the pain of having to watch the effect at such an execrable resolution of just 320x240. Please enjoy!  ;)
Previous files was in common .mkv format, easily playable.
What should I do with these new files in unknown format ?!
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #100 on: July 19, 2019, 06:43:40 pm »
So the output is "known" by the microcontroller , nothing new ,  but a Siglent or a similar generator is actually measuring the output in some way if you load it down ?
About this you don't find anything in manuals .

 Well, the microcontroller will certainly 'know' what the output voltage is supposed to be. All that is required is an additional input from a current sensor to be able to calculate the load impedance and the resulting voltage. If it isn't mentioned in the Siglent manuals (the same cannot be said for the Feeltech manuals[1]), then it isn't a feature of the generator.

 I only mentioned these possible features on the basis of hypothesis from the feeling that radiolistener (and many others) may have been spoilt by such features actually being implemented in the more expensive models, particularly Keysight products, otherwise why the complaint about this halving of the set Vpp when connected to a matching load?

 I honestly don't know of any signal generators that do calculate the load impedance for display to the operator (or, optionally, compensate for its effect on the output voltage in order to keep it at the set p-p voltage - given enough system resources in the generator, anything is possible when backed by a generous R&D budget).

[1] In the manuals for the FY6600 and 6800 models, they both mention a non-existent 10Vpp limit in the 10 to 20MHz range when, in fact, the 20Vpp limit (on sine and square waves at least) actually runs all the way from zero to 20MHz inclusive before dropping straight down to the 5Vpp limit of the opamp which drives the THS3002i which is bypassed by a relay in the frequency range beyond the 20MHz limit. Getting "back on topic", It's quite possible that the same error has been duplicated in the FY6900's manual.

JBG


 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #101 on: July 19, 2019, 06:54:57 pm »
I've (hopefully this time!) attached higher definition movie files of the traces I posted in my previous two postings mainly to reduce the pain of having to watch the effect at such an execrable resolution of just 320x240. Please enjoy!  ;)
Previous files was in common .mkv format, easily playable.
What should I do with these new files in unknown format ?!

 Hi Jacon,

 You had me worried for a moment. I think you may have skipped a step this time round. I'd zipped each one individually using Ark. The files are mkv type as before and, just for good measure, I downloaded them to make sure that they hadn't been got at in any way. I got back exactly what I'd uploaded. They should play just fine once they've been extracted. :)

 The only difference this time round being that I couldn't figure out how to access the pkzip option menu to choose "store", so there's a modicum of compression used this time round. Possibly the reason the others played ok as zip files is because there hadn't been any compression allowing your media player to recognise them as mkvs and play them without you actually extracting them.

JBG
« Last Edit: July 19, 2019, 07:01:08 pm by Johnny B Good »
 

Offline Jacon

  • Contributor
  • Posts: 32
  • Country: pl
Re: Fy6800 vs Fy6900
« Reply #102 on: July 19, 2019, 07:05:52 pm »
OK - done  ;)
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #103 on: July 19, 2019, 09:39:35 pm »
It has an output resistance of 50 ohms.
And the amplitude is set without load.

In reality "without load" condition is impossible. Amplitude with no load doesn't have sense, you cannot create such condition for high frequency. As you know, even open BNC connector has some impedance. In order to measure amplitude, you're always needs to apply some load. Any measurement equipment has impedance and when you connect it to generator, it will make load.

The standard impedance for high frequency measurements is 50 Ohm. Almost all high frequency measurement equipment has 50 Ohm impedance. So, if signal generator shows amplitude for random high resistance load (this is what HiZ exactly means), you're needs to always recalculate these random "volts" to standard volts. Because "HiZ" voltage is completely useless and don't have sense for real measurements.

This is why "HiZ" amplitude is completely useless indication. Frankly speaking, this is complete bullshit. These "HiZ" random volts for random impedance can be used just for marketing purposes in order to misleading those peoples who don't have knowledge and don't know Ohms law.  :bullshit:


« Last Edit: July 19, 2019, 10:30:57 pm by radiolistener »
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #104 on: July 19, 2019, 09:58:17 pm »
For instance you can use a generator with an impedance of 75 ohm to drive a 50 ohm line, allowing for the additional 1.94dB drop (a 60% drop versus the matched case of a 50% drop).

If you're using non standard load, you can easily recalculate amplitude when you know 50 Ohm load based amplitude. With HiZ you will stuck, because there is no actual HiZ in reality. There is always some impedance on the output connector. Even if you BNC is open it still have some impedance, which depends on the frequency. HiZ doesn't exists in reality, so this "HiZ" amplitude is not "HiZ", it is acutally amplitude for some high random impedance. And this is why these "HiZ" volts are random.

The fancy and more expensive signal generators may well offer such a feature. Considering your question, they probably do and possibly by monitoring the current versus voltage output to calculate the actual impedance it is connected to so as to leave the operator a hand free to scratch their balls.

All that is required is an additional input from a current sensor to be able to calculate the load impedance and the resulting voltage.

There is no need to "monitor the current versus voltage output". No need for sensors. If signal generator has 50 Ohm output impedance, it will automatically keep "current versus voltage". The same as simple resistor doesn't need any kind of sensors and "monitor the current versus voltage" in order to keep it's resistance properly. This is simple Ohms law!

I = U/R

There is no need to monitor for current and voltage, the current will be automatically adjusted to the voltage, according to the Ohm's law. And you can simply add your load impedance and get current correction. Since almost all RF equipment has 50 Ohm connectors, you're don't needs to think about it, just use standard 50-ohm impedance voltage.

You can easy calculate dBm power value from 50 Ohm voltage. For HiZ it even doesn't have sense, just because you cannot measure power on random HiZ impedance.

This will turns into problem if you're using so called "HiZ amplitude". In such case it will turns into:

I = U / [random high impedance]

If you will try to convert it to dBm power, it leads to:

P = U^2 / [random high impedance] = [random power value dBm]

This is why HiZ amplitude in context of signal generator for MHz frequencies is complete bullshit:horse:


Personally speaking, I'm rather glad that the Chinese designers of cheap affordable T&M kit have avoided this insult to the intelligence of their hobbyist target market demographic by not adding such unnecessary "Bells and Whistles"

Actually these Chinese guys added "Bells and Whistles", such as useless "HiZ amplitude". It makes hard to use this signal generator, because you're always needs to recalculate real amplitude to these random volts and it needs to re-check real amplitude with measurement equipment in order to avoid confuse.

But you didn't answer on my question - is it possible to recalibrate FY6600 in such way? To show standard 50 Ohm amplitude. It will make life more easy. I hear that there is possible amplitude calibration. So, may be it can be done with proper amplitude calibration for standard 50 Ohm load?

Just think about some special multimeter which show non standard voltage for "spherical horse in the vacuum" model. And you're needs to multiply it's result by sqrt(35) in order to get standard voltage. It's just awful. The same thing with this "HiZ amplitude". This is how this "feature" looks like from the user's point of view.  :-//

I remember that some people mention that there is some attenuator in the FY6600 frontend, which unfortunately didn't properly matched to 50 Ohm due to poor design, so it may leads to issues with 50 Ohm voltage calibration. Is this true?

Why developers of FY6600 are trying to make life difficult by inventing this random "HiZ amplitude" instead of using standard 50 Ohm voltage which is used everywhere? Is this just attempt to hide some critical fail in hardware design?

I just don't understand - why?  :-\
« Last Edit: July 19, 2019, 10:55:16 pm by radiolistener »
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #105 on: July 19, 2019, 11:54:25 pm »
Calibrating the voltage setting for the unloaded condition is the most logical choice (it's very easy to check this well defined unloaded voltage output).

This is not logical and completely useless. Even more, such calibration is completely incorrect. Just because it requires to connect voltage meter to the output connector. Your voltmeter will change this impedance. And your voltage measurement will be actual for specific impedance which is a combination of output generator impedance and your voltmeter input impedance. You will lost your calibration just when you detach your voltmeter from output connector. It will leads to significant change of impedance on the output connector and as result voltage will be changed.

So, this so called "calibration" for "HiZ amplitude" will be lost just when you disconnect your voltmeter from the output connector of your generator.  :-DD

The other issue is that when you use voltmeter with input impedance different than 50 Ohm with 50 ohm coax cable, or just with a piece of wire, it will leads to impedance mismatch and wave reflections. As result your voltmeter will give you incorrect voltage.

In order to avoid such issues with voltage variation due to impedance changes, you're needs to calibrate it with voltmeter which has 50 Ohm imput. It means that all voltage measurements will be 50-ohm impedace based and cannot be applied for so called "HiZ amplitude".  :popcorn:

I can say more. If you're using "HiZ amplitude", there is no way to get known RF power level for calibration. Because HiZ means high resistance (infinite resistance in ideal case), so it will leads to infinite power for any voltage  :-DD
« Last Edit: July 20, 2019, 12:05:22 am by radiolistener »
 

Offline bdunham7

  • Frequent Contributor
  • **
  • Posts: 330
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #106 on: July 20, 2019, 12:02:08 am »
It has an output resistance of 50 ohms.
And the amplitude is set without load.

In reality "without load" condition is impossible. Amplitude with no load doesn't have sense, you cannot create such condition for high frequency. As you know, even open BNC connector has some impedance. In order to measure amplitude, you're always needs to apply some load. Any measurement equipment has impedance and when you connect it to generator, it will make load.

The standard impedance for high frequency measurements is 50 Ohm. Almost all high frequency measurement equipment has 50 Ohm impedance. So, if signal generator shows amplitude for random high resistance load (this is what HiZ exactly means), you're needs to always recalculate these random "volts" to standard volts. Because "HiZ" voltage is completely useless and don't have sense for real measurements.

This is why "HiZ" amplitude is completely useless indication. Frankly speaking, this is complete bullshit. These "HiZ" random volts for random impedance can be used just for marketing purposes in order to misleading those peoples who don't have knowledge and don't know Ohms law.  :bullshit:

While it's true that 50R is a common impedance used in HF, it isn't completely universal and is only conventional for a limited range of conventional instruments dealing with RF.  Common, yes.  Universal, no.  What you don't seem to understand is that the threshold where transmission lines and 50R impedance become necessary is in the 50-200MHz range.  Below that, depending on line length and input capacitances, it is entirely practical and common to use higher impedance setups.  At 1 MHz you can use banana plugs if you like.

There are many things that you might connect your sig-gen to, and in the case of the FY6x00 series, I'm going to guess that most of them are what you call Hi-Z.  Since the output impedance is 50R, the errors caused by varying between 1M, 10M, or even the common 10K and 47K input impedances of audio equipment, are quite small.  If you have something with say 600R or significant capacitance for your selected frequency, well you'll have to do the math.
 
The following users thanked this post: Johnny B Good

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #107 on: July 20, 2019, 12:14:29 am »
What you don't seem to understand is that the threshold where transmission lines and 50R impedance become necessary is in the 50-200MHz range.

I'm understand it pretty good. Because I was seen how a small impedance mismatch on a 10 cm wire leads to SWR > 1.5. and it happens at 3-5 MHz!

At 50-100 MHz it will become even much more sensitive. With 50-100 MHz even wire shift for 0.01 mm will leads to significant change.

Impedance mismatch is a not big deal at very low frequencies, such as 50 Hz or 1000 Hz. But when you're working with frequencies above 100 kHz it become significant. For 1 MHz and more it is very significant.

This is 60 MHz signal generator and impedance match is very and very critical at such frequencies.

You can do these "HiZ" measurements for sound wave generator, when your output is below 10-20 kHz. But when you're working with 100 kHz and above, such approach is not accepted at all.

No take into account impedance for measurements at 1 MHz and above is complete bullshit.
« Last Edit: July 20, 2019, 12:23:07 am by radiolistener »
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #108 on: July 20, 2019, 12:29:35 am »
the errors caused by varying between 1M, 10M, or even the common 10K and 47K input impedances of audio equipment, are quite small.

This is not audio generator. It works with MHz range signal for which impedance plays very important role.

There is no excuse for "HiZ measurements" for RF signals. This is complete bullshit and even don't try to say the opposite.

First try to find 10 MHz calibration source with 0 dBm power level for your "HiZ" RF voltmeter  :-DD


Since the output impedance is 50R

I have suspicion that there is a serious hardware issue with 50 Ohm impedance. Because I don't see reason to show non-existing voltage for non-existing impedance. If it has 50 Ohm, then just show voltage for 50 Ohm to not ruin Ohm's law! It will be correct measurement and all will be ok.

But for some reason it shows non-existing voltage for non-existing so-called "HiZ" impedance. What is the reason for that?   :-\
« Last Edit: July 20, 2019, 12:54:25 am by radiolistener »
 

Offline bdunham7

  • Frequent Contributor
  • **
  • Posts: 330
  • Country: us
Re: Fy6800 vs Fy6900
« Reply #109 on: July 20, 2019, 03:52:20 am »
You seem to have a lot of criticism of a sub-$100 amateur-grade piece of equipment that you've apparently never seen or touched!  And some interesting ideas about impedance that seem like the ham-radio equivalent of audiophoolery to me--but I'll leave all that alone. 

The FY6x00 series are low-cost AWGs, not serious RF-generators.  The fact that some can stretch all the way to 60MHz doesn't make them suitable for any serious RF work, IMO.  I have other tools for this with better frequency accuracy and lower phase noise--I wouldn't even think of using this tool as serious RF generator and mine only goes to 15Mhz anyway.  I would guess, as I said before, that the vast majority of these are being used with high-impedance loads.  I suspect a lot of them are connected to oscilloscopes and drawing pictures.

Some--and only some--of your comments may make some sense if you are working on RF power systems, but as for low-level signals, it is very common to have an intentional impedance mismatch where a low impedance output drives a higher impedance input.  This is how you keep distortion low, for example. Circuits are commonly designed this way going into the many-MHz and beyond.  Impedance matching has its place, but that place isn't everywhere.
 
The following users thanked this post: Jacon, Johnny B Good

Offline CDaniel

  • Frequent Contributor
  • **
  • Posts: 316
  • Country: ro
Re: Fy6800 vs Fy6900
« Reply #110 on: July 20, 2019, 05:41:26 am »
Bellow 5Vpp the 50 ohm is an output series resistor that limit the current for the op amplifier when you short it ... you can calculate the real voltage for a load .

For a "classic " generator with an output  attenuator you don't even know the series resistor and is variable for every output range ... ok could be calibrated to show correctly for 50ohm load and that's about all . But anyway not so high frequency generators are calibrated the same as FY6600 , for infinite load .
« Last Edit: July 20, 2019, 05:44:35 am by CDaniel »
 
The following users thanked this post: Johnny B Good

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #111 on: July 20, 2019, 07:53:58 am »
You seem to have a lot of criticism of a sub-$100 amateur-grade piece of equipment

this is not criticism of device, this is criticism of wrong way to measure AC voltage for frequencies above 1 MHz.

The FY6x00 series are low-cost AWGs, not serious RF-generators. 

it doesn't matter if it RF or audio grade. If it allows to select voltage, this is should be real voltage!

When you use so-called "HiZ" voltage for 10 MHz signal, this is something like voltage applied to "spherical horse in the vaccuum" which doesn't exists in reality  :-DD

you can replace the horse with a cow if you wish


What Z do you mean when you talking about HiZ? Infinite? 100 MOhm? 1 MOhm? 10 kOhm? 100 Ohm? or may be 1 Ohm?

100 pF capacitor has about 159 Ohm impedance at 10 MHz. 159 Ohm is HiZ or LowZ?

« Last Edit: July 20, 2019, 08:27:44 am by radiolistener »
 

Offline pantelei4

  • Regular Contributor
  • *
  • Posts: 90
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #112 on: July 20, 2019, 10:01:23 am »
this is not criticism of device, this is criticism of wrong way to measure AC voltage for frequencies above 1 MHz.
The device does not measure the output voltage.
 
The following users thanked this post: Johnny B Good

Offline CDaniel

  • Frequent Contributor
  • **
  • Posts: 316
  • Country: ro
Re: Fy6800 vs Fy6900
« Reply #113 on: July 20, 2019, 01:41:46 pm »
He doesn't seem to understand that no usual generator is measuring the output , so even if it's calibrated for 50 ohm or whatever you may choose , you must be certain that the load impedance  is exactly that , and not containing stupid capacitors  :(  and inductors that form complex impedance variable with the frequency  :-DD

Sorry , but for measurements you must have a good radio frequency voltmeter ... and not relly on the "magic" numbers a generator is giving to you .
« Last Edit: July 20, 2019, 02:44:38 pm by CDaniel »
 
The following users thanked this post: mnementh, Jacon, Johnny B Good

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #114 on: July 20, 2019, 03:14:21 pm »
The device does not measure the output voltage.

it doesn't measure voltage, but it should provide voltage which is selected on the control panel, if you selected 2 Vpp it should put 2 Vpp on the output. And RF power meter connected to the output should display 10 dBm power level. If it's true, then all works as expected. This is expected behavior.

But I think you will get 3.9 dBm or something like that, it will depends on how FY6600 analog frontend is close to 50 Ohm. That is fail.

Also, there is a problem to calibrate signal generator for these HiZ voltage. This is incorrect way to use 2x of real voltage. Because 2x amplitude will be expected for infinite impedance, which is not the case for FY6600. It doesn't has inifinite impedance, so your calibration will be wrong.
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #115 on: July 20, 2019, 04:52:30 pm »
For instance you can use a generator with an impedance of 75 ohm to drive a 50 ohm line, allowing for the additional 1.94dB drop (a 60% drop versus the matched case of a 50% drop).


But you didn't answer on my question - is it possible to recalibrate FY6600 in such way? To show standard 50 Ohm amplitude. It will make life more easy. I hear that there is possible amplitude calibration. So, may be it can be done with proper amplitude calibration for standard 50 Ohm load?


 You've obviously "Read the Book" but seem to have developed some oddball ideas. Considering that English is not your native tongue and most of the technical literature tends to be published in English, you may have had more of a struggle than native English speakers who, quite frankly will find it difficult enough to comprehend the subtleties of such technical texts despite of the lack of any such "Language Barrier".

 Anyway, all I can advise is that you go through the literature again and take another look whilst keeping in mind what you've learnt here. I'm not going to waste time arguing all the points you've raised here since that would lead to arguments in the vein of "How many Angels can dance on the head of a pin?"

 As for your claim that I didn't answer your question, you are somewhat in error. It's true the short snappy answer you were seeking was buried near the end of my effusive (some might say long winded) reply #94 (fourth paragraph from the bottom) but answer it I did, as you can see from the following extract taken from that reply:-

[QUOTE/]

 In answer to your question... what was it again? Oh yes, the business of the unloaded voltage being a "Chinese Thing"(tm) and the possibility of having the voltage setting expressed as that which a matched load would produce (i.e. display 1Vpp instead of 2Vpp to account for the loading effect of a termination matching the output impedance of the generator).

 The answer in the case of these Feeltech generators is no (at least for the moment - if development of an OSS front panel firmware package ever resumes (seems rather unlikely though) you may well get the opportunity to add this feature to your "Wish List").

[/quote]

 To lend extra clarity, I've rendered the relevant words in bold typeface. The original did not have any parts in bold, I use bold and italics rather sparingly in these posts lest they lose their impact through overuse. In this case, my use of bold text seemed rather appropriate to the occasion ;)

 You've also had several responses to this question along much briefer lines with pantelei4 giving the most concise answer of all (short and to the point  :-+).

 Whilst your assertions appear to be based on the theoretical limitations of generation and measurement of waveforms at high frequencies, such assertions would be more appropriate in a thread such as that linked to below where the facility to generate high enough frequencies to make what you're saying rather more relevant than here where a comparison of two very similar models of cheap ARB generators by Feeltech is being discussed.

https://www.eevblog.com/forum/testgear/siglent-ssg3000x-series-rf-signal-generators/msg1803173/#msg1803173

 The effects you speak of, are likely unmeasurable by most users of these Feeltech arbitrary wave/function generators so are of little significance here.

 The closest a proud owner of any of these generators will get to experiencing the effects you're describing is that of overlooking the need to properly terminate their BNC interconnecting cables. Anyone posting here about their FY6*** not meeting their frequency specification on sine waves will usually accept the friendly advice to terminate the cable with a 50R dummy load and try again, usually without further argument.

 As far as the topic of discussion in this thread goes, we seem to have speculated as much as the scant information on the actual device itself (the new FY6900) goes. It's now just a matter of time waiting for the reviews to appear. Until then, it rather looks like the discussion will remain in hiatus. BTW, having wandered 'back on topic', does anyone have any idea of the likely release date(s) of this latest and greatest from Feeltech (Feelelec)?

JBG
 

Offline Jacon

  • Contributor
  • Posts: 32
  • Country: pl
Re: Fy6800 vs Fy6900
« Reply #116 on: July 20, 2019, 05:13:17 pm »
...
BTW, having wandered 'back on topic', does anyone have any idea of the likely release date(s) of this latest and greatest from Feeltech (Feelelec)?
JBG
According to Banggood FY6900 site, EU -60MHz versions are "in stock" today, shipping in 24h, while US versions
shipping are expected from 28th July  ;)
Overall 102 sold till now.
« Last Edit: July 20, 2019, 05:15:20 pm by Jacon »
 
The following users thanked this post: Johnny B Good

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #117 on: July 20, 2019, 05:47:57 pm »
Anyway, all I can advise is that you go through the literature again and take another look whilst keeping in mind what ou've learnt here.

There is no literature which can approve HiZ amplitude calibration for high frequency 50 Ohm output of signal generator.  :horse:
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #118 on: July 20, 2019, 05:58:19 pm »
The answer in the case of these Feeltech generators is no (at least for the moment - if development of an OSS front panel firmware package ever resumes (seems rather unlikely though) you may well get the opportunity to add this feature to your "Wish List").

Ok, thanks, this is what I'm asked for. I already know it shows incorrect voltage and you're needs to recalculate it each time when you need to setup amplitude. I don't need for explanation, I already know pitfalls due to this bug and know that you can still use it, but needs to take into account this behavior. It will leads to a lot of confusion and a lot of mistakes. The question was if it's possible to fix it. So, the answer is no. This is sad.  :-\
« Last Edit: July 20, 2019, 06:04:00 pm by radiolistener »
 

Offline Andreas

  • Super Contributor
  • ***
  • Posts: 2500
  • Country: de
Re: Fy6800 vs Fy6900
« Reply #119 on: July 20, 2019, 06:03:56 pm »
Why do you complain?

There are more quirks on these cheap hobby generators like
- 80% AM is in reality only 65% and the amplitude is too low.
- when changeing the frequency over USB interface the AM modulation is switched off.

https://www.eevblog.com/forum/testgear/fy6800-dds-signal-generator-questions/msg2502990/#msg2502990

So for the price you will have to arrange with the "features"

with best regards

Andreas
 
The following users thanked this post: Johnny B Good

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #120 on: July 20, 2019, 06:07:32 pm »
Why do you complain?

May be manufacturer will find all these issues and it will be fixed. If you don't complain, then manufacturer even will not know that there is something wrong with their device.   :-//

I just thought to buy this sig-gen, but this "HiZ amplitude" is a real stopper. I'm thinking how I will convert real amplitude to these "HiZ" and will get a lot of mistakes due to that, this HiZ is real head pain.
« Last Edit: July 20, 2019, 06:18:06 pm by radiolistener »
 

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #121 on: July 20, 2019, 06:55:02 pm »
You seem to have a lot of criticism of a sub-$100 amateur-grade piece of equipment that you've apparently never seen or touched!  And some interesting ideas about impedance that seem like the ham-radio equivalent of audiophoolery to me--but I'll leave all that alone. 

The FY6x00 series are low-cost AWGs, not serious RF-generators.  The fact that some can stretch all the way to 60MHz doesn't make them suitable for any serious RF work, IMO.  I have other tools for this with better frequency accuracy and lower phase noise--I wouldn't even think of using this tool as serious RF generator and mine only goes to 15Mhz anyway.  I would guess, as I said before, that the vast majority of these are being used with high-impedance loads.  I suspect a lot of them are connected to oscilloscopes and drawing pictures.

Some--and only some--of your comments may make some sense if you are working on RF power systems, but as for low-level signals, it is very common to have an intentional impedance mismatch where a low impedance output drives a higher impedance input.  This is how you keep distortion low, for example. Circuits are commonly designed this way going into the many-MHz and beyond.  Impedance matching has its place, but that place isn't everywhere.

 Are you thinking what I'm thinking?  >:D

 Those comments are pretty close to my own thoughts on the matter of radiolistener's contributions to this thread.

 radiolistener appears to have a very tenuous grasp of the subject. One give away being his error in referring to a 1Vpp in 50 ohms as 0dBm50 when in fact it's actually very close to +4dBm50. 0dBm50 is represented by a p-p voltage of 634mV (224mV rms).

 The 0dBm600 figure of rms voltage in common use within the audio industry is burned into my mind as 775mV, surprisingly close to a 2Vpp value at 2.191919 Vpp.

 Aside from that goof, he lost all credibility by claiming a VSWR of 1.3 from the effect of a few centimetres of wire (15cm, istr) on a 3.5MHz test signal (or was it 3 to 5MHz? ICBA to go back and check - whichever it was, it makes very little difference).

 My best guess from these clues, is that radiolistener is a shortwave listener with ambitions of becoming a licensed "Radioham", using an HF transceiver as his shortwave radio come signal generator. How often do we see measured VSWR mentioned in the context of signal generators (especially the low end variety we're currently discussing)? The only other kit where I see mention of directional couplers and VSWR as a matter of course, are Vector Network Analysers (VNA).

 The suspicion that he's been experimenting at the bottom end of the 80 metre ham band leads me to put two and two together and get four (five, if they're large values of two). I may be well off the mark but that's my best guess for what it's worth. >:D

JBG
 
The following users thanked this post: Jacon

Offline CDaniel

  • Frequent Contributor
  • **
  • Posts: 316
  • Country: ro
Re: Fy6800 vs Fy6900
« Reply #122 on: July 20, 2019, 07:29:55 pm »
Why do you complain?

May be manufacturer will find all these issues and it will be fixed. If you don't complain, then manufacturer even will not know that there is something wrong with their device.   :-//

I just thought to buy this sig-gen, but this "HiZ amplitude" is a real stopper. I'm thinking how I will convert real amplitude to these "HiZ" and will get a lot of mistakes due to that, this HiZ is real head pain.

You better buy a proper HF voltmeter and stop complaining about this non sense ...
After all this talking nobody understand what do you want actually . Every generator has an output attenuator , so the series resistance will cause errors if the load is not exactly as expected .
 
The following users thanked this post: Jacon, Johnny B Good

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #123 on: July 20, 2019, 08:03:15 pm »
...
BTW, having wandered 'back on topic', does anyone have any idea of the likely release date(s) of this latest and greatest from Feeltech (Feelelec)?
JBG
According to Banggood FY6900 site, EU -60MHz versions are "in stock" today, shipping in 24h, while US versions
shipping are expected from 28th July  ;)
Overall 102 sold till now.

 Thank you for that information, Jacon.

 It looks like we might get some answers to our speculations very soon (Blogs, Youtube video reviews etc). I've just had a search for reviews and youtube videos but, as was the case a few hours earlier when I last checked, the only results were seller advertising and nothing on youtube. This thread is actually the third hit on the first page of a duckduckgo search! ::)

JBG
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #124 on: July 20, 2019, 08:10:40 pm »
radiolistener appears to have a very tenuous grasp of the subject. One give away being his error in referring to a 1Vpp in 50 ohms as 0dBm50 when in fact it's actually very close to +4dBm50. 0dBm50 is represented by a p-p voltage of 634mV (224mV rms).

This is LIE! I never referred 1 Vpp as 0 dBm. I referred 2 Vpp as 10 dBm. Also I indirectly mentioned 1 Vpp as 3.9 dBm.

So, YOU'RE LIAR!   >:(

Since you don't know exact dBm value for 1 Vpp at 50 Ohm, I can say: 1 Vpp = 3.9794 dBm at 50 Ohm

Also you're wrong, here is your mistake: 0 dBm is NOT 634 mV, actually it is 632.4555 mVpp or 316.2278 mVpk.

The 0dBm600 figure of rms voltage in common use within the audio industry is burned into my mind as 775mV, surprisingly close to a 2Vpp value at 2.191919 Vpp.

Here is also your mistake, 0 dBm at 600 Ohm load is not "2.191919 Vpp", actually it is 2.19089023002066 Vpp  :-//

My best guess from these clues, is that radiolistener is a shortwave listener with ambitions of becoming a licensed "Radioham"

here is again your mistake, I already have license and callsign for at least several years.

The suspicion that he's been experimenting at the bottom end of the 80 metre ham band leads me to put two and two together and get four (five, if they're large values of two). I may be well off the mark but that's my best guess for what it's worth.

This is again your mistake. Currently I'm experimenting with direct sampling SDR on FPGA which directly captures ether with 122.880 MHz ADC and performs digital down conversion. It allows to listen and transmit at any frequency from DC up to 61 MHz. Also I'm experimenting with 144 MHz band.

If you're thinking that you can hang noodles on my ears, you're also wrong. You can tell your tales that impedance doesn't matter for 60 MHz generator to someone other who don't know about it, but don't tell me that.

I just asked you if it's possible to fix this issue in the generator. I didn't asked you to explain if I need this or not. I already know what I need. And I expected simple answer from you, one of the following:
- "yes it is possible, here is how it can be done <...>"
- "no, it is not possible, but it will be available soon"

I already got your answer - "This is not possible. And nobody is working on this at the moment". So, please stop lie and manipulating.

Best regards
« Last Edit: July 20, 2019, 08:39:51 pm by radiolistener »
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #125 on: July 20, 2019, 08:24:44 pm »
Every generator has an output attenuator , so the series resistance will cause errors if the load is not exactly as expected .

If you don't want errors, then do not connect load which impedance doesn't match with generator output. This is pretty easy to understand. This is why almost all high frequency signal generators have standard 50 Ohm output. For what reason you're mention output attenuator? It is not intended to make errors, it is intended to reduce signal level.

Guys, I understand, this is your business to sell these cheap devices, but don't present everything as if this device has no problems. Just ask your developers to fix issues. This is what buyers expecting from you. That's it. Thanks

Best regards

« Last Edit: July 20, 2019, 08:29:35 pm by radiolistener »
 

Online Simon

  • Global Moderator
  • *****
  • Posts: 14447
  • Country: gb
  • Did that just blow up? No? might work after all !!
    • Simon's Electronics
Re: Fy6800 vs Fy6900
« Reply #126 on: July 20, 2019, 08:35:37 pm »
Just calm down!
 
The following users thanked this post: Johnny B Good

Offline Johnny B Good

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: gb
Re: Fy6800 vs Fy6900
« Reply #127 on: July 20, 2019, 09:02:55 pm »
radiolistener appears to have a very tenuous grasp of the subject. One give away being his error in referring to a 1Vpp in 50 ohms as 0dBm50 when in fact it's actually very close to +4dBm50. 0dBm50 is represented by a p-p voltage of 634mV (224mV rms).

This is LIE! I never referred 1 Vpp as 0 dBm. I referred 2 Vpp as 10 dBm. Also I indirectly mentioned 1 Vpp as 3.9 dBm.

So, YOU'RE LIAR!   >:(

Since you don't know exact dBm value for 1 Vpp at 50 Ohm, I can say: 1 Vpp = 3.9794 dBm at 50 Ohm

Also you're wrong, here is your mistake: 0 dBm is NOT 634 mV, actually it is 632.4555 mVpp or 316.2278 mVpk.

The 0dBm600 figure of rms voltage in common use within the audio industry is burned into my mind as 775mV, surprisingly close to a 2Vpp value at 2.191919 Vpp.

Here is also your mistake, 0 dBm at 600 Ohm load is not "2.191919 Vpp", actually it is 2.19089023002066 Vpp  :-//

My best guess from these clues, is that radiolistener is a shortwave listener with ambitions of becoming a licensed "Radioham"

here is again your mistake, I already have license and callsign for at least several years.

The suspicion that he's been experimenting at the bottom end of the 80 metre ham band leads me to put two and two together and get four (five, if they're large values of two). I may be well off the mark but that's my best guess for what it's worth.

This is again your mistake. Currently I'm experimenting with direct sampling SDR on FPGA which directly captures ether with 122.880 MHz ADC and performs digital down conversion. It allows to listen and transmit at any frequency from DC up to 61 MHz. Also I'm experimenting with 144 MHz band.

If you're thinking that you can hang noodles on my ears, you're also wrong. You can tell your tales that impedance doesn't matter for 60 MHz generator to someone other who don't know about it, but don't tell me that.

I just asked you if it's possible to fix this issue in the generator. I didn't asked you to explain if I need this or not. I already know what I need. And I expected simple answer from you, one of the following:
- "yes it is possible, here is how it can be done <...>"
- "no, it is not possible, but it will be available soon"

I already got your answer - "this is not possible". So, please stop lie and manipulating.

Best regards

 Whoa there, Neddy!

 That's a rather unwarranted overreaction if ever I saw one! I'll admit to mis-remembering the figures you'd actually used (even the best of us can fall foul of such errors and for that, you get an apology) but calling someone a liar straight off the bat without considering the possibility of a simple mistake is a rather undignified response to say the least.

 Who knows? Perhaps I'd subconsciously wilfully mis-remembered those figures but I certainly hadn't intended to. I guess I just had to "lance this particular boil" and release the pent up venom that had obviously been building up.

 I just hadn't expected this event to occur so soon. I'm sure you've left a lasting impression on the other members participating in this thread. Sadly for you, it's not one to be proud of.

JBG
 

Offline radiolistener

  • Super Contributor
  • ***
  • Posts: 1074
  • Country: ua
Re: Fy6800 vs Fy6900
« Reply #128 on: July 20, 2019, 10:26:41 pm »
That's a rather unwarranted overreaction if ever I saw one! I'll admit to mis-remembering the figures you'd actually used (even the best of us can fall foul of such errors and for that, you get an apology) but calling someone a liar straight off the bat without considering the possibility of a simple mistake is a rather undignified response to say the least.

 Who knows? Perhaps I'd subconsciously wilfully mis-remembered those figures but I certainly hadn't intended to. I guess I just had to "lance this particular boil" and release the pent up venom that had obviously been building up.

The reason why you're lying doesn't matter. You do that, you were caught lying and there is no reason to believe you anymore. As you know you have trust just once.

You're tried to change conversation subject from technical details to the discussion of personalities a lot of times in this topic. You know very well who are doing such tricks, they doing it because they are unable to argue in discussion and so they are switching to talking about personalities in order hide their fail. After all, I don't see the reason to continue this discussion. It looks like your sales method are completely failed. You're lost me as a buyer, I will not buy feeltech production after conversation with you, so good luck with other users.
 
The following users thanked this post: Johnny B Good


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf