Author Topic: 4ch 100MHz 1GS/s per channel cheap-o-scope  (Read 12611 times)

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Offline MrWolf

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4ch 100MHz 1GS/s per channel cheap-o-scope
« on: November 02, 2016, 10:26:18 am »
Hello,

usually I mess around with low frequency and have been spoiled by having excessive resolution of waveforms. But specific task has emerged that will require 4 channels, at least 100MHz and most importantly at least 1GS/s on all channels at the same time.
Currently I have 25MHz PicoScopes and no real complaints about them. They do take abuse and software is feature-packed (FFT!). Initially I wanted to buy PicoScope 2408B or Rigol DS1054Z  (and hack it), until I realized that instead of being cheap-o-scopes these are actually fake-o-scopes because they are only 250MS/s on 4ch and 100MHz - which is basically a sad joke, not scope.
After quite a bit of search I found that only (?) cheap-o-scope doing full 1GS/s on 4 channels is Tek TBS1104, but it hopelessly outdated otherwise (low memory etc).
Proper PicoScopes start at €2,795.00 with 6402C, but this is out of budget currently (about €1500 max).
I do like (toy-o-scope  :P) GW INSTEK GDS-2204E (has FFT!) but its only doing 500MS/s with all ch in use.
Currently almost out of ideas. Maybe buy two of something 2ch with trigger in-outs and  sync but this will probably go out of budget.
Used stuff do not like, only maybe refurbished with new knobs. Do not like knobs that have been rubbed by someone else :(
Maybe TBS1104 low mem is not an issue at full tilt since there is only 10 samples per wfm anyway?
Almost forgot - there must be option do display non-interpolated raw waveform. 10 samples per wfm is not much and when interpolated all the useful info will be lost for good.
« Last Edit: November 02, 2016, 10:28:19 am by MrWolf »
 

Offline rf-loop

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #1 on: November 02, 2016, 10:44:12 am »
SDS2104X all 4 channels on 1GSa/s for all channel. 2 channels on, 2GSa/ch
Also enough memory for most use,
Powerful fast segmented memory acquisition.
Always backround working Waveform history buffer.
In your budget due to factory offer.
Also it keep raw data independent of interpolation and display settings.

If practice and theory is not equal it tells that used application of theory is wrong or the theory itself is wrong.
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Offline TopLoser

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #2 on: November 02, 2016, 11:02:45 am »
Keysight DSOX2004 hacked up to 200MHz does 1GS/s on all 4 channels and is way under your budget.
 

Online Ice-Tea

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #3 on: November 02, 2016, 11:10:13 am »
Or you could, you know, get an older scope from a reputed brand with the specs you need...

*whistles innocently* :popcorn:

Offline MrWolf

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #4 on: November 02, 2016, 11:11:56 am »
Thats good news about SDS2104X, I actually looked at it but important info in datasheet was only in fine print (missed that) so I decided that it is probably only 500MS/s and went searching further. Since this is selling point they should make it more prominent in datasheet I think...
Also I think people should stop buying substandard fake-o-scopes and just push them out of the market. Dave makes some good points in this old video:

Sadly seems that many newbies do not realize this and go for products based on analog front end rating only (almost did fall for that).

 

Offline JPortici

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #5 on: November 02, 2016, 11:26:38 am »
but they are cheap! and can get the job done.
And they are 100 MHz scopes.
You don't use a 100 MHz tool for a 100 MHz signal. 5-10 times the bandwidth and the adequate rise time if you want to have a good approximation of a square wave.
 

Online tggzzz

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #6 on: November 02, 2016, 11:41:50 am »
But specific task has emerged that will require 4 channels, at least 100MHz and most importantly at least 1GS/s on all channels at the same time.

Why is 1GS/s important to you, given the 100MHz spec? Often it is better to concentrate on the risetime.

You don't mention whether the signals are repetitive or single-shot, nor whether it is necessary to export waveforms to other devices.
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline rf-loop

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #7 on: November 02, 2016, 11:46:28 am »
Thats good news about SDS2104X, I actually looked at it but important info in datasheet was only in fine print (missed that) so I decided that it is probably only 500MS/s and went searching further. Since this is selling point they should make it more prominent in datasheet I think...


No. Absolutely not. It have 1GSa/s for every single channel simultaneously when all 4 channels are on.

There is 2 channel group.
I
CH1 + CH2 they have one 2x1GSa  Analog devices ADC. If one of these channel is in use ADC work in single 2GSa/s mode.  140M memory.
II
CH2 + CH3 they have one 2x1GSa  Analog devices ADC. If one of these channel is in use ADC work in single 2GSa/s mode. 140M memory. 140 for one channel and 70 per channel if both are in use.

If there is in group I or II both channel on, then other group can use only 1GSa/s even if in this group only one channel is in use.
(principle is that channels in use at same time, can use only same speed)

If select group I  one channel in use and group II  one channel... both can use 2GSa/s and both have max 140M acquistion memory (+ more for waveform history buffer, what principle is explained more in SDS1000X thread. Same principle in SDS2000X but 2kX have lot of more processing power and memory)

Also about many information in web. You need really be careful because most of informations are Obsolete. And if you look some videos, even from Dave, be careful and keep in mind there is many kind of "user errors".   Also many times there have been perhaps even many FW updates after these some videos.








« Last Edit: November 02, 2016, 12:04:45 pm by rf-loop »
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Offline rsjsouza

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #8 on: November 02, 2016, 12:01:02 pm »
Another alternative is the DS4014E, which goes up to 2GSPS per channel and is around €1.6k.

If I am not mistaken, the GW Instek GDS2104A has 1GSPS per channel at 100MHz. At €1.3k it fits in your budget.
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Offline MrWolf

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #9 on: November 02, 2016, 12:22:43 pm »
but they are cheap! and can get the job done.
And they are 100 MHz scopes.
You don't use a 100 MHz tool for a 100 MHz signal. 5-10 times the bandwidth and the adequate rise time if you want to have a good approximation of a square wave.

No plans to use it for digital signal tinkering. Analog sine-waves in 50...100MHz range with phase shifts involved. Basically want to learn about transmission line stuff in freq area where lines are getting reasonably short for experimenting. If I can get general picture at 4ch 1GS and pinpoint more exactly at 2ch 2GS will be more-less on top of things. With stable signals can even enable ETS and get hires. However I do realize that this is absolute minumum tech for this... But you do not spend big bucks in area where you are novice. Upgrade to GHz gear after year or two learning curve...
 

Offline MrWolf

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #10 on: November 02, 2016, 12:43:24 pm »
You don't mention whether the signals are repetitive or single-shot, nor whether it is necessary to export waveforms to other devices.

CSV export would not hurt. Signals analog, modulated, repetitive eg transmission line suff. Replys got me thinking maybe should go for 200MHz, 1GS. In some cases seems to fit in budget.
 

Online Ice-Tea

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #11 on: November 02, 2016, 12:55:01 pm »
Or, you know, 1GHz, 4GSa/S

*Whistles some more*

Offline Fungus

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #12 on: November 02, 2016, 01:03:49 pm »
I wanted to buy PicoScope 2408B or Rigol DS1054Z  (and hack it), until I realized that instead of being cheap-o-scopes these are actually fake-o-scopes because they are only 250MS/s on 4ch and 100MHz

Later on you'll find out that 250MS/s is the correct sample rate for sampling 100MHz signals and then you'll realize that your post is embarrassing.


at least 100MHz and most importantly at least 1GS/s on all channels at the same time.

That specification makes no sense.
 

Online tggzzz

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #13 on: November 02, 2016, 01:27:04 pm »
but they are cheap! and can get the job done.
And they are 100 MHz scopes.
You don't use a 100 MHz tool for a 100 MHz signal. 5-10 times the bandwidth and the adequate rise time if you want to have a good approximation of a square wave.

No plans to use it for digital signal tinkering. Analog sine-waves in 50...100MHz range with phase shifts involved. Basically want to learn about transmission line stuff in freq area where lines are getting reasonably short for experimenting. If I can get general picture at 4ch 1GS and pinpoint more exactly at 2ch 2GS will be more-less on top of things. With stable signals can even enable ETS and get hires. However I do realize that this is absolute minumum tech for this... But you do not spend big bucks in area where you are novice. Upgrade to GHz gear after year or two learning curve...

In that case you really want a TDR. A Tektronix 1502 will enable you to resolve small impedance changes 2cm apart. That's a system risetime of  140ps, roughly equivalent to 2.5GHz - and you get a 50ps step generator included.

See https://entertaininghacks.wordpress.com/2016/08/30/a-traditional-tdr-cable-tester-with-2cm-resolution/ for pretty pictures.

Its primary use is finding small and large problems in cables and connectors and PCBs, or cable length, or dielectric constant. Let me know offline how much you would pay for a working example, because I have a spare one for sale :) I'll see if anyone wants it at a hamfest on Sunday

N.B. my spare is the "normal" variant, calibrated in feet and inches, sigh!
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline EEVblog

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #14 on: November 02, 2016, 01:46:53 pm »
Will you ever use the full 100MHz bandwidth on all 4 channel simultaneously?
 

Offline MrWolf

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #15 on: November 02, 2016, 05:16:47 pm »
That specification makes no sense.

Has it occurred to you that I have actually tested my scenarios at lower frequencies with exactly matching analog freq / sample ratio? Findings conform exactly to that old EEVBlog video. "Fatal data loss" occurs at about 10 samples per wave for basic sine wave. So in short you are saying that owner of this blog is talking BS in that video. Way to go.

Will you ever use the full 100MHz bandwidth on all 4 channel simultaneously?

Barely enough for starters. Monitoring for both voltage and current tends to eat up channels fast...
 

Offline MrWolf

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #16 on: November 02, 2016, 05:38:19 pm »
Or, you know, 1GHz, 4GSa/S

Advice is correct but as ex-CCCP citizen Im used to making fine carpentry with axe ;)
 

Offline JPortici

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #17 on: November 02, 2016, 06:33:36 pm »
oh get that sweet lecroy of his already ;)
 

Offline MrWolf

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #18 on: November 02, 2016, 06:56:26 pm »
oh get that sweet lecroy of his already ;)

This kind of stuff will come after I had my way with something fresh and probably chinese. Also not very portable... forgot to mention portability req because all the low-end stuff is pretty portable nowdays...
...ok who Im fooling - Its too big to hide from my wife in small apartment   :-//
 

Offline JPortici

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #19 on: November 02, 2016, 07:14:13 pm »
the lecroy can be disguised as a vintage tv  :-+
or a futuristic microwave  :-//
get creative

anyway measuring sine wave phase shift.. is a scope the correct tool? and i think you'd need a lot higher bandwidth than the signal as i believe the input antialiasing filter is not gaussian.. sure is not on old DSOs or cheap modern DSOs, with lower samplerate-bandwidth ratio.

Is the input channel bode plot even provided on higher end scopes?
 

Online Ice-Tea

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #20 on: November 02, 2016, 07:27:58 pm »
oh get that sweet lecroy of his already ;)

This kind of stuff will come after I had my way with something fresh and probably chinese. Also not very portable... forgot to mention portability req because all the low-end stuff is pretty portable nowdays...
...ok who Im fooling - Its too big to hide from my wife in small apartment   :-//

But... It has a carying handle! And you can use it as a boat anchor!

I see your point, though ;)

Offline Fungus

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #21 on: November 02, 2016, 07:54:43 pm »
That specification makes no sense.

Has it occurred to you that I have actually tested my scenarios at lower frequencies with exactly matching analog freq / sample ratio? Findings conform exactly to that old EEVBlog video. "Fatal data loss" occurs at about 10 samples per wave for basic sine wave. So in short you are saying that owner of this blog is talking BS in that video. Way to go.

Which video? What 'scope?
 

Offline rsjsouza

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #22 on: November 02, 2016, 08:15:41 pm »
That specification makes no sense.

Has it occurred to you that I have actually tested my scenarios at lower frequencies with exactly matching analog freq / sample ratio? Findings conform exactly to that old EEVBlog video. "Fatal data loss" occurs at about 10 samples per wave for basic sine wave. So in short you are saying that owner of this blog is talking BS in that video. Way to go.

Which video? What 'scope?
Fungus, the video is linked above.

Regarding analog bandwidth versus digital sampling rate, there are many discussions in this forum (here, here and here for example) with varying degrees of experience and opinion, with the offending pissing contest and mud flinging... :)
 
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Online nctnico

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #23 on: November 02, 2016, 09:09:25 pm »
Used stuff do not like, only maybe refurbished with new knobs. Do not like knobs that have been rubbed by someone else :(
Just clean the knobs and they'll look as new. Easy job for the amount of money you save. Perhaps your best paid job ever! If you don't need protocol decoding then there are many choices out there on the second hand market.
Quote
Almost forgot - there must be option do display non-interpolated raw waveform. 10 samples per wfm is not much and when interpolated all the useful info will be lost for good.
Sorry but no information gets lost due to interpolation. Interpolation is there to make the signal interpretable with our eyes. Just read about the Nyquist theory and you'll learn that 10 times oversampling is overkill and you won't get any extra information. Just more money gone from your wallet.

Perhaps you could elaborate on your other requirements. You mention FFT but are they other things which are important like connectivity, math, measurements, filtering, etc?
« Last Edit: November 02, 2016, 09:13:18 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Someone

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #24 on: November 02, 2016, 11:18:12 pm »
That specification makes no sense.

Has it occurred to you that I have actually tested my scenarios at lower frequencies with exactly matching analog freq / sample ratio? Findings conform exactly to that old EEVBlog video. "Fatal data loss" occurs at about 10 samples per wave for basic sine wave. So in short you are saying that owner of this blog is talking BS in that video. Way to go.

Which video? What 'scope?
Fungus, the video is linked above.

Regarding analog bandwidth versus digital sampling rate, there are many discussions in this forum (here, here and here for example) with varying degrees of experience and opinion, with the offending pissing contest and mud flinging... :)
 
You forgot this epic thread too: https://www.eevblog.com/forum/testgear/will-keysight-upgrade-the-2000-3000t-x-series-oscilloscopes-within-a-few-months/?all

Almost forgot - there must be option do display non-interpolated raw waveform. 10 samples per wfm is not much and when interpolated all the useful info will be lost for good.
Sorry but no information gets lost due to interpolation. Interpolation is there to make the signal interpretable with our eyes. Just read about the Nyquist theory and you'll learn that 10 times oversampling is overkill and you won't get any extra information. Just more money gone from your wallet.
I would like to live in your magical world where measurements have no noise in them and the front end antialias filters are perfect, the rest of us will happily continue buying scopes with sample rates 5-10x higher than required by nyquist (or more!).
 
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Online nctnico

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #25 on: November 03, 2016, 09:29:49 am »
Almost forgot - there must be option do display non-interpolated raw waveform. 10 samples per wfm is not much and when interpolated all the useful info will be lost for good.
Sorry but no information gets lost due to interpolation. Interpolation is there to make the signal interpretable with our eyes. Just read about the Nyquist theory and you'll learn that 10 times oversampling is overkill and you won't get any extra information. Just more money gone from your wallet.
I would like to live in your magical world where measurements have no noise in them and the front end antialias filters are perfect, the rest of us will happily continue buying scopes with sample rates 5-10x higher than required by nyquist (or more!).
You forget the filtering provided by the probing solution (every probing solution has a limited bandwidth). If your signal has so much noise that it is becoming a problem then you have different challenges to measure it because with or without interpolation or oversampling the noise isn't going away. AND you have to realise you can never get an accurate representation of a signal on an oscilloscope anyway. Limited bandwidth, probe influences (loading), variations in the frequency response, phase delays, limited resolution, non-linearities all sit between the signal and what is shown on your screen. All in all an oscilloscope is good for getting an idea on what a signal looks like especially in the lower end segment and with general purpose probes.
« Last Edit: November 03, 2016, 09:38:50 am by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Someone

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #26 on: November 03, 2016, 09:47:08 am »
Almost forgot - there must be option do display non-interpolated raw waveform. 10 samples per wfm is not much and when interpolated all the useful info will be lost for good.
Sorry but no information gets lost due to interpolation. Interpolation is there to make the signal interpretable with our eyes. Just read about the Nyquist theory and you'll learn that 10 times oversampling is overkill and you won't get any extra information. Just more money gone from your wallet.
I would like to live in your magical world where measurements have no noise in them and the front end antialias filters are perfect, the rest of us will happily continue buying scopes with sample rates 5-10x higher than required by nyquist (or more!).
You forget the filtering provided by the probing solution (every probing solution has a limited bandwidth). If your signal has so much noise that it is becoming a problem then you have different challenges to measure it because with or without interpolation or oversampling the noise isn't going away.
The bandwidth is not hard limited which is whats required for sampling, there is a diminishing return as the sample rate is increased and aliasing reduces but its common to have a much higher sample rate than strictly required. Its even mentioned in the opening paragraph about antialiasing filters on wikipedia:
https://en.wikipedia.org/wiki/Anti-aliasing_filter
And secondly its not the signal noise but the measurement noise, a higher sample rate still reduces noise in the measurement even if its far beyond whats needed to reproduce the frequency components. You can gloat all you like about your understanding of nyquist theorem but the theorem has many assumptions which do not apply in the real world where the rest of us live and work. So perhaps you could contribute something practical to the discussion rather than your ego stroking theoretical arguments which are repeatedly torn down.
 

Offline tautech

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #27 on: November 03, 2016, 12:30:48 pm »
SDS2104X all 4 channels on 1GSa/s for all channel. 2 channels on, 2GSa/ch
Also enough memory for most use,
Powerful fast segmented memory acquisition.
Always backround working Waveform history buffer.
In your budget due to factory offer.
Also it keep raw data independent of interpolation and display settings.
In fact much better than in MrWolf's budget, € 1405 for the SDS2104X (100 MHz 4 Ch) and with the promotion for that price the SDS2204X (200 MHz) is supplied.
So if only 100 MHz is required, purchase a SDS2074X for € 1099 and the SDS2104X is supplied.
1 GSa/s (all channels) and 140 M memory depth, nothing else comes near for the price.
http://www.siglenteu.com/pdxx.aspx?id=1195&T=2&tid=1


I'm told there are some noticeable performance improvements in the next soon to released FW.

Edit.
Link added
« Last Edit: November 03, 2016, 01:14:56 pm by tautech »
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Online nctnico

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #28 on: November 04, 2016, 01:10:08 am »
So perhaps you could contribute something practical to the discussion rather than your ego stroking theoretical arguments which are repeatedly torn down.
Perhaps I should have noted that most of my paid projects involve sampling and some are data acquisition systems (oscilloscopes without knobs and fancy user interface). Nyquist's theory is the basis for all these projects in order to get a good balance between sampling frequency and anti-aliasing filtering. But you don't have to take my word for it. Keysight has a nice document about it: cp.literature.agilent.com/litweb/pdf/5989-5732EN.pdf. On page 5 you can read that 8x sampling versus 4x sampling shows minimal differences (you have to look really hard).

The summary:
As you’ve read in this application note, there’s more to oscilloscope signal fidelity than just sample rate. In some cases a lower-sample-rate scope may produce more accurate measurement results. To satisfy Nyquist criteria, you need a scope that samples at least three to five times higher than the scope’s bandwidth  specification, depending on the scope’s frequency roll-off characteristics. Achieving higher sample rates often requires that scope vendors interleave multiple  real-time ADCs. But if real-time interleaving is employed, it is critical that the interleaved ADCs be vertically matched and the timing of phase-delayed clocking  must be precise. It should be noted that the problem is not the number of interleaved ADCs; the issue is the level of precision of interleaving. Otherwise, Nyquist’s second rule (equally-spaced samples) can be violated, thereby producing distortion and often negating the expected benefit of higher sample rates.

Back to the OP's original question: in order to sample a signal with frequency components up to 100MHz a 100MHz scope with 500Ms/s is perfectly suitable.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Someone

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #29 on: November 04, 2016, 02:06:58 am »
Back to the OP's original question: in order to sample a signal with frequency components up to 100MHz a 100MHz scope with 500Ms/s is perfectly suitable.
The OP is wishing to measure small phase shifts which the additional samples will help for, they asked for specific features and backed it up with a legitimate explanation of why.

I don't care what your experience or credentials are, because you're wrong.
 

Online nctnico

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #30 on: November 04, 2016, 02:24:00 am »
Back to the OP's original question: in order to sample a signal with frequency components up to 100MHz a 100MHz scope with 500Ms/s is perfectly suitable.
The OP is wishing to measure small phase shifts which the additional samples will help for, they asked for specific features and backed it up with a legitimate explanation of why.
If you'd read the paper provided by Keysight you'd known that 500Ms/s + interpolation for 100MHz signals gives you a much higher timing accuracy than the sampling rate would suggest. In the paper Keysight shows their DSO7000 series which uses 2Gs/s to get 10s of ps timing resolution as an example. The answer is right in your face and you still don't see it!  :palm:
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Someone

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #31 on: November 04, 2016, 07:23:56 am »
Back to the OP's original question: in order to sample a signal with frequency components up to 100MHz a 100MHz scope with 500Ms/s is perfectly suitable.
The OP is wishing to measure small phase shifts which the additional samples will help for, they asked for specific features and backed it up with a legitimate explanation of why.
If you'd read the paper provided by Keysight you'd known that 500Ms/s + interpolation for 100MHz signals gives you a much higher timing accuracy than the sampling rate would suggest. In the paper Keysight shows their DSO7000 series which uses 2Gs/s to get 10s of ps timing resolution as an example. The answer is right in your face and you still don't see it!  :palm:
Or you could come back to the real world (marketing material is easy to make with happy numbers) and actually measure these things, you've had plenty of chances to back down so here is a real measurement on 2 different scopes where they are measuring the skew of two channels. The probes are connected to slew limited logic signals with edges around 5ns which is close to the OPs 100MHz signals, and the scopes are in normal run mode with their onboard measurements providing the data (you can do better with offline analysis).

Thats what you call a correlation, as predicted by noise reduction. Real world once again meets with theory when that includes real world effects.
 

Online nctnico

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #32 on: November 04, 2016, 10:16:38 am »
The OP specified 1Gs/s which probably means he wants/needs a 1ns time resolution. That is easy to achieve with 500Ms/s + interpolation. If noise is a problem you can use frequency domain filtering (input filtering, bandwidth limiting, hires mode) or time domain filtering using averaging. A much more important feature will be the short term stability of the sample clock.

Sure you can move the goal posts and show a much better and >20 times more expensive oscilloscope with a much higher samplerate has a much higher time resolution but that is a) not what the OP is asking for b) rather obvious and nobody will claim anything different.
« Last Edit: November 04, 2016, 10:21:25 am by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Someone

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #33 on: November 04, 2016, 10:29:46 am »
The OP specified 1Gs/s which probably means he wants/needs a 1ns time resolution. That is easy to achieve with 500Ms/s + interpolation. If noise is a problem you can use frequency domain filtering (input filtering, bandwidth limiting, hires mode) or time domain filtering using averaging. A much more important feature will be the short term stability of the sample clock.
Try it with a scope and see what result you get. Averaging or high res did not reduce the noise below that of the full sample rate. Pretty pictures and accurate measurements are two different things.
Sure you can move the goal posts and show a much better and >20 times more expensive oscilloscope with a much higher samplerate has a much higher time resolution but that is a) not what the OP is asking for b) rather obvious and nobody will claim anything different.
The example is a 100MHz band limited signal into a 200MHz 4GSa/s scope and showing how the noise in the time measurement increases as you reduce the sample rate through and below 1GSa/s. Thats the conditions the OP is asking about and what you claimed repeatedly would make no difference, and there for all to see (and reproduce to prove to themselves) is the result that increasing sample rate improves the measurement of relative time. Instead of theory and your promises how about you present some data?
 

Offline MrWolf

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #34 on: November 04, 2016, 10:33:58 am »
I will tell a story: First I had old russian analog scope. Real straight forward piece of equipment like AK47. But I needed more channels so went for PicoScopes. Soon had two of them with 4ch + 16digital in total, was rather pleased with initial tests (but no idea about digital trickery involved behind the scenes). Afterwards started building some experimental analog contraption involving heavily non-linear components. When started testing almost went mad. It did not produce designed signals no matter what I did, non-linearities were all wrong. For days I debugged and tested and calculated until finally I found the culprit deep in the PS software menus... Sin(x)/x on by default. After switching it OFF discovered that contraption was working as designed from the day 1. So maybe one can get away with 2.5 samples per wfm (PS actually had 4 at max freq, all ch in use) for very well known situations... but for heavily experimental stuff only thing that counts is raw data, period. When you start replacing raw data with math fantasy you usually get string theory or something, not maglev trains :)
Edit: Remembered that there was yet another culprit, "resolution enhancement", I turned it on because is seemed cool to have 12bits instead of 8 :) But this was quick to pinpoint because at low sample rate per wfm all left was straight line on screen :P
« Last Edit: November 04, 2016, 11:03:18 am by MrWolf »
 

Offline rf-loop

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #35 on: November 04, 2016, 11:07:37 am »
Quote
only thing that counts is raw data, period. When you start replacing raw data with math fantasy you usually get string theory or something, not maglev trains :)

 :clap:
If practice and theory is not equal it tells that used application of theory is wrong or the theory itself is wrong.
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Online nctnico

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #36 on: November 04, 2016, 11:33:26 am »
Edit: Remembered that there was yet another culprit, "resolution enhancement", I turned it on because is seemed cool to have 12bits instead of 8 :) But this was quick to pinpoint because at low sample rate per wfm all left was straight line on screen :P
In my experience with Picoscopes their resolution enhancement mode can have all kinds of strange effects. However I don't buy sin x/x interpolation was/is the problem because it is a well proven technology in general but you'll have to keep in mind that the samplerate must be high enough to capture the highest frequency component of the signal. Keeping peak-detect on helps a lot to prevent strange signals showing on the screen due to aliasing.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline rsjsouza

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #37 on: November 04, 2016, 11:55:18 am »
Quote
only thing that counts is raw data, period. When you start replacing raw data with math fantasy you usually get string theory or something, not maglev trains :)

 :clap:
I had a good laugh at that. Excellent way to put it!  :-DD
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Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...
 

Offline Fungus

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #38 on: November 04, 2016, 12:07:35 pm »
Screenshots or it isn't true.
 

Offline MrWolf

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #39 on: November 04, 2016, 12:22:22 pm »
samplerate must be high enough to capture the highest frequency component of the signal
It was rather complex signal. Main point was that without interpolation I immediately realized that I have not enough raw data and tweaked stuff accordingly. Interpolation masked lack of data. My "contraption" is long gone, but just for kicks I might try to reproduce this when I get new signal gen and scope. Seems every scope has its own character and bag of tricks:



So long story short and my advice for other beginners. Start with all fancy stuff OFF.

Edit: Would be cool feature to display data points on top of interpolated signal with different color. This way you get nice "expensive look" but can instantly decide if you have enough data or not.
« Last Edit: November 04, 2016, 12:38:04 pm by MrWolf »
 

Online nctnico

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #40 on: November 04, 2016, 02:10:44 pm »
The OP specified 1Gs/s which probably means he wants/needs a 1ns time resolution. That is easy to achieve with 500Ms/s + interpolation. If noise is a problem you can use frequency domain filtering (input filtering, bandwidth limiting, hires mode) or time domain filtering using averaging. A much more important feature will be the short term stability of the sample clock.
Try it with a scope and see what result you get. Averaging or high res did not reduce the noise below that of the full sample rate. Pretty pictures and accurate measurements are two different things.
Lets put it to the test then with a GDS-2204E, a HP4421B RF generator (with a stable timebase) set to 101MHz, RF splitter, 2 identical cables, a 33cm cable and some tees & terminators.
First check skew between channel 1 and 2 with averaging (32 cycles) on:

Now with the 33cm extra cable for channel 2
1Gs/s without averaging:

1Gs/s with averaging (32 cycles):

500Ms/s without averaging:

500Ms/s with averaging  (32 cycles):


I think it is clear that the samplerate doesn't affect the time resolution at the same time/div setting and averaging does improve time delay measurement (less noise). It all has to do with the data which is used to do the calculation. HP/Agilent/Keysight scopes typically use the screen data and not the actual samples to do waveform calculations so a lot of the initial accuracy of the samples gets lost in translation at longer time/div settings (Tektronix has a nice application bash note on that BTW) and hence the yellow line in your graph slopes down at first but then levels. It may be different on a Lecroy or Tektronix scope.
« Last Edit: November 04, 2016, 04:58:08 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Someone

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #41 on: November 05, 2016, 01:53:14 am »
I think it is clear that the samplerate doesn't affect the time resolution at the same time/div setting and averaging does improve time delay measurement (less noise). It all has to do with the data which is used to do the calculation. HP/Agilent/Keysight scopes typically use the screen data and not the actual samples to do waveform calculations so a lot of the initial accuracy of the samples gets lost in translation at longer time/div settings (Tektronix has a nice application bash note on that BTW) and hence the yellow line in your graph slopes down at first but then levels. It may be different on a Lecroy or Tektronix scope.
Determining these sorts of small delays between signals requires some form of reconstruction to the the picosecond resolution from "only" a nanosecond sample rate, so its impossible the measurement is directly from the raw points of the data. Better would be to use the triggers of the channels as in a hardware timer, but it would still need some interpolation to resolve the picosecond resolutions. The 3024A is limited to only 2ns/div and the measurement noise is related to the reconstructed signal as you change up through 5ns/div and 10ns/div it roughly doubles at each step.

The 54845A was used as an example as you can change the sample rate manually without changing the timebase, with a 50 ohm source the signal noise should be lower and we could expect a reduction in the measured time noise. It was particularly interesting as there was a repeatable bump in the measurement noise at 4GSa/s so your comparisons of just 2 different sampling rates may be hitting against some similar oddity in the way the channels are sampled at different rates for interleaving.
 

Offline Someone

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #42 on: November 05, 2016, 05:53:14 am »
Swept a whole bunch of different configurations and picked up on some further gotchas around the averaging and quantising. The reconstruction of the waveform can use the extra bits from averaging acquisitions but the measurement engines are heavily quantised. On the Agilent 3024A the delay time measurement is quantised to a single pixel (best case 32ps), while on the above captures of the GW Instek GDS-2204E it appears to be quantised to at least 5ps. Once the acquisition averaging reduces the noise below this quantisation then the measurement engines can report a zero standard deviation when the signal sits in a single quantised value, sitting close to a transition you can get measurements reporting silly things like just femtoseconds of noise. This caused interesting sequences of measurements which didnt fit to funnel plot, exposing their measurement biases. Quantisation in each step of the process is causing some really ugly answers.
 

Offline MrWolf

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #43 on: November 09, 2016, 02:45:41 pm »
Conundrum is solved. If found no 4ch 100-200MHz all-channel 1GS/s scope in my price range without severe limitations in one or another area. So instead I bought "disposable-cheap" 4ch scope and two 2-channel signal generators (can be synced!). After applying some slight tweaks I will have 4ch 25MHz complex waveform read/write and 4ch ~100MHz sine read/write capability. Quiz: what exact products I did choose while not abusing the piggy bank of about 1500€ :P
 

Offline rsjsouza

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #44 on: November 10, 2016, 10:05:07 pm »
Quiz: what exact products I did choose while not abusing the piggy bank of about 1500€ :P
Let me guess: a Hantek 6104BC and two MHS-5200A-25M?  :-DD
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Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...
 

Offline MrWolf

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Re: 4ch 100MHz 1GS/s per channel cheap-o-scope
« Reply #45 on: November 18, 2016, 11:08:32 am »
Well by "not abusing" I meant it was a clean kill. Not stretching or any other way of mutilation.
2x Siglent SDG2042X
1x Rigol DS1054Z
Even 25EUR left for testing-time beer case :D
What I did find out so far:
SDG2042X -  :-+  :clap:
DS1054Z -  :--  :-BROKE  :palm:  |O
Noone to blame but myself, rf-loop did discover long time ago that latter is just a hack...
but Dave said "just buy it" so....  :-//
 


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