Author Topic: BG7TBL FA1 and FA2 frequency analyzers  (Read 8186 times)

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Offline cncjerry

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #50 on: October 13, 2019, 07:36:06 am »
In addition to the FA2 I'm looking at the FSA3011 frequency stability analyzer.  But then I ran across this thing:

https://www.ebay.com/itm/DC5V-0-2A-1M-100M-simple-phase-noise-tester-noise-tester/122376396168?hash=item1c7e339d88:g:RbwAAOSw3v5YtmXN&redirect=mobile

This is listed as a "simple phase noise tester".  It has an input and output sma and is used with a spectrum analyzer.   I doubt very much it is really a phase noise tester.  I've used John's PN.exe with my spectrum analyzer but that is very limited to the SA noise floor unlike real PN test sets that go down to -170dBm.  So what is this thing doing?

Thanks,

Jerry
 

Offline jpb

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #51 on: October 13, 2019, 01:46:40 pm »
In addition to the FA2 I'm looking at the FSA3011 frequency stability analyzer.  But then I ran across this thing:

https://www.ebay.com/itm/DC5V-0-2A-1M-100M-simple-phase-noise-tester-noise-tester/122376396168?hash=item1c7e339d88:g:RbwAAOSw3v5YtmXN&redirect=mobile

This is listed as a "simple phase noise tester".  It has an input and output sma and is used with a spectrum analyzer.   I doubt very much it is really a phase noise tester.  I've used John's PN.exe with my spectrum analyzer but that is very limited to the SA noise floor unlike real PN test sets that go down to -170dBm.  So what is this thing doing?

Thanks,

Jerry
That has been around a while and has been discussed on this forum before, though I now can't find the relevant post. It is a frequency multiplier (with corresponding phase noise multiplication) so you can view the phase noise of say a 10MHz oscillator up at 2.6GHz.
Unfortunately it is very hard to get any details from the seller. I tried sending the seller a message and got no response.

I'm interested in the FSA3011 but it is rather pricey so it would be good to know if it works as well as advertised. If it was around half the price I might take a punt on it but at £400 plus import duty I'd prefer to spend money on a good quality USB audio interface and put together my own system. I'm a bit frustrated at present because my current setup with a good counter and using a DDS as a local oscillator is a bit too noise at around 10^-11 at 1s.
 

Offline cncjerry

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #52 on: October 13, 2019, 08:07:10 pm »
I think I am going to have to just bite the bullet and purchase a phase noise test set of some type.  I'll have all the stability test equipment I need shortly as I have another board coming.  But I also have a Cs, about 10 Rb units and two GPSDOs so stability-wise I'm covered. But I wish there was a way to measure close-in phase noise, like from 0 to 10Khz (but out to 100Khz) within the HF spectrum for less than $500.  Every time I look for a test set they are mucho $$$$.  I have used John's PN tool with my spectrum analyzers but they don't compare to the oscillators used today.  This all started when I built the N2PK VNA and I started a second one using a better oscillator.  But I couldn't measure the improvement other than a slightly better noise floor.

Not to get off topic, but if someone has an idea on how to inexpensively measure close in PN for less than $500, I would appreciate a PM.  I looked at a filter method where you used the signal in test (or another oscillator) out of phase to cancel the primary leaving just the noise.  I cant remember the challenges around that system.

By the way, I thought TVB and Corby on time-nuts tested the FSA3011.  I think the comments were inline with those here that it was a little expensive by 2x and he couldn't get it to meet the specs but I thought that was an early comment.  I would have to go back and see if there were other notes.

The FA2 is a great unit for the money.  Not good for 1pps measuring or comparison a/b of low frequencies unless there are hidden features.

Jerry
 
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Offline jpb

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #53 on: October 13, 2019, 09:22:03 pm »
Re the FSA3011
Thank you for the reference to time nuts - I found this :
https://lists.febo.com/pipermail/time-nuts_lists.febo.com/2019-August/097304.html
I don't know if there is any further info later than August.

Going back a bit earlier the main one is in July:
https://www.mail-archive.com/time-nuts@lists.febo.com/msg04082.html

It does look as if it is over-priced for the claimed results. Also, if it doesn't live up to the specs then there is a danger that it fails to be good enough so it is a lot of money to  spend on something that may not be able to measure because the noise floor is too high.
« Last Edit: October 13, 2019, 09:29:21 pm by jpb »
 

Offline bnz

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #54 on: October 14, 2019, 06:02:21 am »
Some info on the FSA3011 can be found at:
www.leapsecond.com/pages/FSA3011
 
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Offline edigi

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #55 on: October 15, 2019, 05:34:42 pm »
Some more photos and measurement of own reference with 10s gate time.
I've noticed that OCXO is very sensitive to any vibration or movement but if it's kept stable it's pretty good.
« Last Edit: October 15, 2019, 05:41:23 pm by edigi »
 
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Offline Electro Fan

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #56 on: October 15, 2019, 08:15:35 pm »
Those displayed numbers look pretty good.

On a related note, not sure that the info is reliable or even that it matters but fwiw, I asked an eBay seller (who sells/sold both the FA-2 and a 2018-06-05 BG7TBL GPSDO) which provides greater accuracy for a 10 MHz signal - and the answer was the BG7TBL GPSDO. 

I'm pretty happy with the BG7TBL GPSDO and I'm going to try the FA-2 using the BG7TBL GPSDO to provide the FA-2 with a 10 MHz reference and then see what the FA-2 displays for various frequencies fed from other source devices and compare those results to a couple other counters also taking the 10 MHz ref signal from the BG7TBL GPSDO and the other same source devices. Kinda hard to know what causes what but maybe it will be possible to isolate a few variables and learn something. When TEA syndrome strikes it can be hard to shake. 
« Last Edit: October 15, 2019, 08:18:17 pm by Electro Fan »
 

Offline Diabolo

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #57 on: October 16, 2019, 01:00:13 pm »
Hello,


On the PCB front, we notice that D1 to D6 are not in place, and that the board has the location of 3 unassembled switches.

What can these missing elements serve?

Datasheet OCXO CTS 196xxxx : http://www.xtal.cc/UploadFiles/Product/20161101163222_40783.pdf


Cdlt,
Diabolo
« Last Edit: October 16, 2019, 01:17:13 pm by Diabolo »
 

Offline picburner

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #58 on: October 16, 2019, 07:29:47 pm »
@ edigi: the buzzer will be very weak with the protective label still attached.
 

Offline mark03

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #59 on: October 17, 2019, 05:37:18 pm »
I think I am going to have to just bite the bullet and purchase a phase noise test set of some type.  I'll have all the stability test equipment I need shortly as I have another board coming.  But I also have a Cs, about 10 Rb units and two GPSDOs so stability-wise I'm covered. But I wish there was a way to measure close-in phase noise, like from 0 to 10Khz (but out to 100Khz) within the HF spectrum for less than $500.  Every time I look for a test set they are mucho $$$$.

Something like this, perhaps?  http://www.wenzel.com/documents/measuringphasenoise.htm
 

Offline edigi

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #60 on: October 18, 2019, 07:38:56 am »
Buzzer is my least concern (btw. it's loud enough even with protective seal on, unless you work in very noisy environment that is not too healthy).

The CH2 input impedance can be fixed with a 56 Ohm through hole resistor (we need through hole here to have some inductance that cancels it out on higher frequencies as the chip used for prescaler has 50 Ohm input impedance there; I've used a 1/8W version with short leads but I could not check the exact crossover point). While this fixes the input impedance of CH2, there is still some frequency shown for CH2 even nothing connected. In the prescaler output there should be a schmitt trigger but it's either not doing correctly its job or its something else and while driving the divided down signal connected to the main PCB it picks up noise from the prescaler.
Note: If you've checked my photos the meter is very well shielded (including front and back side PCB) so the signal that is measured cannot originate outside of the box (I've tested it even in the cellar, where even my mobile has trouble picking up any signal).
The prescaler is a /256 one (checked with DSO as I could not identify the chip). 6 wires are connecting the prescaler with the main PCB, 2 for power, 1 for the divided signal and 3 I can guess only. 2 probably is used to control division ratio (typically this kind of control is used with high divide ratio chips; probably not used here) and 1 wire that has a very strange, long burst of pulses like PWM. I suspect this has something to do with the shown frequency and probably this is what picked up by the prescaler chip. Otherwise I don't know the purpose.

The input impedance of CH2 was easy to fix (although requires some soldering experience) but I don't know what to do with CH1 without schematic or any kind  of documentation. CH1 is actually more problematic from this perspective as worst case I can swap the prescaler for CH2 (I have PCB that goes up to 11 GHz and probably even more from HMC chip series so I could even gain in the upper range with this kind of swap).
CH1 can handle quite low level signal till 270 MHz (even if frequency cannot be measured power is shown thanks to the AD8307) and a bit more if signal level is increased with sensitivity for frequency measurement dropping quite sharp from 280 MHz upwards.

Note: I've updated this post to reflect correct information based on what is learned from the standalone BG7TBL prescaler (see later posts).
« Last Edit: October 31, 2019, 09:00:55 am by edigi »
 

Offline cncjerry

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #61 on: October 19, 2019, 08:33:23 pm »
I think I am going to have to just bite the bullet and purchase a phase noise test set of some type.  I'll have all the stability test equipment I need shortly as I have another board coming.  But I also have a Cs, about 10 Rb units and two GPSDOs so stability-wise I'm covered. But I wish there was a way to measure close-in phase noise, like from 0 to 10Khz (but out to 100Khz) within the HF spectrum for less than $500.  Every time I look for a test set they are mucho $$$$.

Something like this, perhaps?  http://www.wenzel.com/documents/measuringphasenoise.htm


The challenge with this and others is that you need a reference source VCO that is as good as or better than the DUT or OUT, ha.  I've played with these as they are easy to wire up on a breadboard.  Really easy to test 10Mhz as I have a bunch of decent, better than average, HP 10811's plus the one in my Cs beam for a reference.  Then you just need two switch the PLL loop constants to test 1hz, 10, 1K, 10K, etc. and using an external sound card adapter, you can get out to 100k using Spectrum Lab.

There is another version that uses a Johnson counter or quadrature hybrid (twisted wire quad hybrid by Breed et al, if IIRC) and then you get the I/Q advantages and you only need the source.  Now that one I haven't wired up but was thinking about it lately.

I guess what I'm looking for is some type of external board, already put together with high quality, high-speed ADCs, all the transformers and mixers architected like the one you suggested or the one I mentioned, for less than $500.  I can put it all together but the drawings are way over simplified because you should condition the input (those circuits are available) and I don't know if you need zero crossing for this or not.

Thanks

 

Offline jpb

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #62 on: October 20, 2019, 08:21:26 pm »
you should condition the input (those circuits are available) and I don't know if you need zero crossing for this or not.

For my experiments I've been conditioning the inputs using LTC6957 demo boards. They are expensive relative to the core chips but you get nice sma inputs/outputs.
https://www.digikey.com/product-detail/en/linear-technology-analog-devices/DC1766A-A/DC1766A-A-ND/3973495
 

Offline edigi

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #63 on: October 22, 2019, 04:39:04 pm »
I could get my hands on second copy of FA2 and naturally I've immediately started to check the input impedance.
1) CH2 is not 50 Ohm but some higher impedance so it's the same (but this is easy to fix)
2) The impedance displayed for CH2 cannot be changed with RST+MODE
3) The impedance displayed for CH1 can be changed with RST+MODE, clicking can be heard (which I could not hear earlier) and indeed the impedance is changed

Based on this it seem that my copy has some SW issue (has probably earlier wrong SW).
Is anyone aware of SW update possibility for FA2? Was it ever possible for FA1?
I fear the whole SW is closed and not even binary is available...
It seems that I have bad luck.

I've attached pictures of my wrong FA2 variant showing impedance for CH2.
« Last Edit: October 22, 2019, 06:36:11 pm by edigi »
 

Offline cncjerry

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #64 on: October 23, 2019, 11:01:03 pm »
you should condition the input (those circuits are available) and I don't know if you need zero crossing for this or not.

For my experiments I've been conditioning the inputs using LTC6957 demo boards. They are expensive relative to the core chips but you get nice sma inputs/outputs.
https://www.digikey.com/product-detail/en/linear-technology-analog-devices/DC1766A-A/DC1766A-A-ND/3973495

Looking at those boards, are there two inputs outputs?  It looked like from the data sheet it was an in+ and in- with corresponding outputs.

thanks - a little pricey.
 

Offline jpb

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #65 on: October 24, 2019, 03:18:19 pm »
you should condition the input (those circuits are available) and I don't know if you need zero crossing for this or not.

For my experiments I've been conditioning the inputs using LTC6957 demo boards. They are expensive relative to the core chips but you get nice sma inputs/outputs.
https://www.digikey.com/product-detail/en/linear-technology-analog-devices/DC1766A-A/DC1766A-A-ND/3973495

Looking at those boards, are there two inputs outputs?  It looked like from the data sheet it was an in+ and in- with corresponding outputs.

thanks - a little pricey.

Yes the inputs are + and - (so only one of them). I put a 50 ohm termination on the one I don't use. They are pricey (sadly) - it would be much cheaper to do your own pcb for the chips - I wanted to have something to go quickly. I was only planning to use one of them but then later I decided I needed a second (for source and reference).
There are two outputs (for the CMOS version I have) so you can supply two instruments or get a noise floor for the ref/dut inputs.
 

Offline wolfp

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #66 on: October 26, 2019, 08:55:09 am »
My FA2 arrived yesterday. The first thing I did was translating the manual into understandable language.
Then I connected the FA2 to a Leo Bodnar GPSDO waited an hour and started measurements at 100MHz on CH1. The deviation was 1.4Hz - not bad for such a cheap device. The test is still running to observe the stability.
The next I will do is to compare the power-measurement of CH1 to a precision-generator.

BTW: The display of my FA2 seems only to be illuminated after warm-up of the VCOCXO.

Wolfgang
 

Offline edigi

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #67 on: October 27, 2019, 06:46:46 am »
BTW: The display of my FA2 seems only to be illuminated after warm-up of the VCOCXO.

That's yet another (3rd variant) then.

Btw. The aging of the internal OCXO in the first week is around 50-100mHz (in the first days above 10mHz/day) thus precise measurement can be done only with external reference.
I didn't even bother to set the compensation in the first 2 weeks (partly because the hole at the back is not perfectly aligned with the adjustment potentiometer that makes harder to use the flat type of screwdriver).
With aging the frequency of the internal reference tends to decrease.
 

Offline Diabolo

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #68 on: October 29, 2019, 02:28:42 pm »
Actually the first clue that something is not right with the impedance of FA2 was that CH2 is showing a frequency even without anything connected. I've checked this even with a 50 Ohm termination and it's still showing some frequency that is actually not even varying too much (I'm far from anything to cause such interference).
Is this issue present only with my copy?

I've also made a longer (overnight) and a shorter measurement of it's own reference (OCXO is still in an early phase of aging). Results attached.

Hello,

I received an FA-2. Channel 2 also gives me the frequency 56xx mhz. If I shunt the CH2 input this frequency is always displayed. I think of an internal phenomenon of radiation captured when CH2 has no signal at the entrance. Maybe a shield is needed on some of the electronics. Overall this FA2 works very well and suits me.

Cdlt,
Diabolo
 

Offline wolfp

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #69 on: October 29, 2019, 05:26:14 pm »
Imho it is not unusual that these prescalers oscillate near the upper frequency if no signal is connected. I observed this also with other devices.
 

Offline wolfp

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #70 on: October 29, 2019, 05:30:05 pm »
Concerning the illumination of the display: Its not a feature but a bug. There seems to be a bad connection to the display.
 

Offline edigi

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #71 on: October 29, 2019, 06:20:55 pm »
It's pretty much common with FA2 that it displays something using CH2, maybe it's possible to get rid via connecting some small capacitor to the input of the next chip.
I have however many Fuji and Hittite prescalers and all of them work without any such phenomenon.

I've managed to make progress with the help of the seller in the wrong impedance of CH1 (which is more an issue than what signal is shown when nothing is connected).
Most probably I have a faulty relay switch. It does not switch no matter if it gets 5V (in case of 50R) or 0V (in case of 1MR).
Maybe the package had a harsh shipping or the relay switch was faulty already when it was built in and went unnoticed as even if someone checks if the unit works, it requires a bit more check if input impedance is correct or not...

I hope that the seller comes up with some reasonable solution, as even if I could replace the relay switch (probably as I have desoldering station) maybe it's not so cheap and easy to get 1 of such relay switch.
« Last Edit: October 31, 2019, 08:56:57 am by edigi »
 

Offline edigi

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #72 on: October 29, 2019, 07:08:22 pm »
Actually for the record if someone faces a similar issue later on I attach a picture of the PCB and a short description that contains a significant amount of guessing.
 
Both the low and the high side of the  relay switch is controlled (the 0 volt is actually zero, if you add some load as otherwise it's more like floating). The low side control comes via R76 and Q3 (this is certain).  The high side control comes from Q1 and that ugly long line. D6 is probably for reverse current protection (the relay switch has coil).
The AD8307 measuring the power is connected together with the 50 Ohm load so it's not independent. My guess is that D9 switches the LPF.
I was wrong earlier that the relay switch has also some other purpose. No, its sole purpose is switching on the AD8307 together with the 50 Ohm input load.
U11 is probably for input signal amplification (could be easily checked with scope but sorry I was lazy).
 


Offline edigi

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Re: BG7TBL FA1 and FA2 frequency analyzers
« Reply #74 on: October 30, 2019, 01:24:16 pm »
Thanks. I've already bought a replacement in the local shop that I regularly use (+ more spares of them in Ebay, as it's cheaper but it takes weeks til it arrives). Local shop was more expensive, I've got 2 for around the same price as in your link for 5.
We'll see during the evening, as what still troubles me why is it possible change the impedance shown on the LCD for SMA input in my case?  :-//
That's why I actually didn't want to post an update till I know more.
Btw. I never know what's available in these local shops as they are so old school that they don't even have a web page.
When I was looking for a 0603 SMD resistor they looked on me like I'm from the moon. This time when I've presented my need for this relay switch I've got it like when a roll is requested in the bakery shop...
 


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