Author Topic: Two Tone Test with Scope and SA  (Read 2565 times)

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Offline joeqsmith

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Re: Two Tone Test with Scope and SA
« Reply #25 on: August 01, 2020, 12:30:22 am »
doubt this will be of any help but here is my HP33120A & 2024  set to 10.0 & 10.1MHz with minicircuits splitter.

Shown on my SignalHound  in swept mode and my vintage HP3589A.     HP supports a narrow band sweep but I think this is outside of it's usable range.     

For fun also shown with the HP3589A using 10MHz and 10.0001MHz.   
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 

Offline David Hess

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Re: Two Tone Test with Scope and SA
« Reply #26 on: August 01, 2020, 02:58:13 am »
I'm not sure I did everything right. I combined the two signals from the generator with a T-piece and terminated them with 50 Ohm on the oscilloscope.

Think you want to resistively combine the two sources for the tones unless you can combine them internally like the Siglent. A resistive "T" should work, think this has 16.7 series ohms on each leg to maintain 50 ohms on all three ports.

You have to be very careful combining the signals because the output amplifiers of the signal generators will produce the same distortion products that you are testing for if they are driven with the other signal.

Ideally a combiner which provides isolation between the input ports is required but it is usually sufficient to pad each output with an attenuator and use minimum loss resistive divider.

Update: I meant to type "minimum loss resistive combiner".
« Last Edit: August 01, 2020, 03:26:05 am by David Hess »
 

Offline mawyatt

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Re: Two Tone Test with Scope and SA
« Reply #27 on: August 01, 2020, 03:12:58 am »
I'm not sure I did everything right. I combined the two signals from the generator with a T-piece and terminated them with 50 Ohm on the oscilloscope.

Think you want to resistively combine the two sources for the tones unless you can combine them internally like the Siglent. A resistive "T" should work, think this has 16.7 series ohms on each leg to maintain 50 ohms on all three ports.

You have to be very careful combining the signals because the output amplifiers of the signal generators will produce the same distortion products that you are testing for if they are driven with the other signal.



Ideally a combiner which provides isolation between the input ports is required but it is usually sufficient to pad each output with an attenuator and use minimum loss resistive divider.

That's why you want to look at this with a SA, to see if the AWG is causing any self-generated IMD issues when resistively combined outputs, if so then add some pads. The Siglent AWG has this nice feature where the two tone combining is done internally (digitally I suspect).

Best,
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Online TheSteve

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Re: Two Tone Test with Scope and SA
« Reply #28 on: August 01, 2020, 06:35:29 am »
Keysight 33522B generating 10 kHz and 10.1 kHz @ 1 VPP, combined via resistive network, 50 ohms everywhere.
FFT on Keysight MSOX3024T and SA on Keysight N9918A(20 dB external atten used here, also at the very bottom of its freq range).





Same test repeated at 10 MHz and 10.1 MHz:




« Last Edit: August 01, 2020, 07:11:30 am by TheSteve »
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Offline PeDre

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Re: Two Tone Test with Scope and SA
« Reply #29 on: August 01, 2020, 09:07:48 am »
I have now combined the signals with 16 ohm resistors on a breadboard, and again terminated with 50 ohm. The spectrum analyzer measures 10 dBm for one tone, the oscilloscope measures 1 Volt peak.
Attached are the measurements for 10 kHz, 100 kHz, 1 MHz and 10 MHz. FFT is normal this time, without Max Hold. The small values jump a little bit up and down around 1 dB.

Generator Rigol DG4162
Oscilloscope R&S RTB2004 (200 MHz BW)
Spectrum Analyzer Rigol DSA815 (with external 20 dB Attenuator)

Edit: New DSA815 pictures
« Last Edit: August 03, 2020, 04:24:29 pm by PeDre »
 
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Offline mawyatt

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Re: Two Tone Test with Scope and SA
« Reply #30 on: August 01, 2020, 01:49:39 pm »
I have now combined the signals with 16 ohm resistors on a breadboard, and again terminated with 50 ohm. The spectrum analyzer measures 10 dBm for one tone, the oscilloscope measures 1 Volt peak.
Attached are the measurements for 10 kHz, 100 kHz, 1 MHz and 10 MHz. FFT is normal this time, without Max Hold. The small values jump a little bit up and down around 1 dB.

Generator Rigol DG4162
Oscilloscope R&S RTB2004 (200 MHz BW)
Spectrum Analyzer Rigol DSA815 (with external 20 dB Attenuator)

This shows off the R&S true 10 bit ADC, nice results!!

Best,
Research is like a treasure hunt, you don't know where to look or what you'll find!
~Mike
 
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Offline PeDre

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Re: Two Tone Test with Scope and SA
« Reply #31 on: August 01, 2020, 02:07:56 pm »
And here the Rigol DS1104Z and MSO2302A. I haven't managed to get better settings. The DS1104Z FFT uses the memory, not the screen as source.
« Last Edit: August 01, 2020, 02:12:22 pm by PeDre »
 

Offline mawyatt

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Re: Two Tone Test with Scope and SA
« Reply #32 on: August 01, 2020, 02:24:18 pm »
Keysight 33522B generating 10 kHz and 10.1 kHz @ 1 VPP, combined via resistive network, 50 ohms everywhere.
FFT on Keysight MSOX3024T and SA on Keysight N9918A(20 dB external atten used here, also at the very bottom of its freq range).





Same test repeated at 10 MHz and 10.1 MHz:




The scope results are interesting, they don't show the 2F1-F2 & 2F2-F1 3rd Order IMD products, or they are buried in the noise floor. Seems Keysight is getting more performance out of the 8 bit 5GSPS ADC than I would expect, maybe some sort of manipulation to extend the apparent ADC resolution? Anyway, very nice result for a very nice scope!!

Best,
Research is like a treasure hunt, you don't know where to look or what you'll find!
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Offline mawyatt

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Re: Two Tone Test with Scope and SA
« Reply #33 on: August 01, 2020, 03:29:00 pm »
And here the Rigol DS1104Z and MSO2302A. I haven't managed to get better settings. The DS1104Z FFT uses the memory, not the screen as source.

You need a longer time span to separate these two tones.

Best,
Research is like a treasure hunt, you don't know where to look or what you'll find!
~Mike
 

Offline PeDre

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Re: Two Tone Test with Scope and SA
« Reply #34 on: August 01, 2020, 04:08:56 pm »
And here the Rigol DS1104Z and MSO2302A. I haven't managed to get better settings. The DS1104Z FFT uses the memory, not the screen as source.

You need a longer time span to separate these two tones.

Best,

Then the FFT span is too small and the 10 MHz frequency is out of range. It's the same with the other test frequencies. With a 10 and 11 MHz tone it would probably work, as well as with the Hameg HM2008. The values are in dBV.

Edit: New images added with better settings for 1 khZ and 10 MHz tone.
« Last Edit: August 03, 2020, 09:18:54 am by PeDre »
 

Offline 2N3055

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Re: Two Tone Test with Scope and SA
« Reply #35 on: August 01, 2020, 04:26:31 pm »
10 kHz and 10.1 kHz 0 dBm from SDG6052X with digital WaveCombine.

Keysight MSOX3104T

[attachimg=1]

Picoscope 3406D MSO (8bit)

[attachimg=2]

Picoscope 4262 (16bit)

[attachimg=3]

SDG6000X WaveCombine works quite well for low frequencies.. And Picos are great for this kind of work...
 
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Offline tautech

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Re: Two Tone Test with Scope and SA
« Reply #36 on: August 01, 2020, 07:41:41 pm »
The $499 SDS1104X-E.......

Signal source as previous, SDG2042X + Wave Combine, 0dB into 50 ohms and max everything...mem depth, 1 Mpts FFT......
Averages engaged this time, just 4.









« Last Edit: August 01, 2020, 07:43:55 pm by tautech »
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Offline 2N3055

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Re: Two Tone Test with Scope and SA
« Reply #37 on: August 01, 2020, 07:48:15 pm »
The $499 SDS1104X-E.......
...............

That looks good!
 

Offline tautech

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Re: Two Tone Test with Scope and SA
« Reply #38 on: August 01, 2020, 08:00:54 pm »
The $499 SDS1104X-E.......
...............

That looks good!
They're as good as you drive them.  ;)

Rejected for posting as I didn't take enough time with the settings and particularly not a slow enough timebase:
Compare with last above.



The $379 SDS1202X-E will be next....when I get a chance.
« Last Edit: August 01, 2020, 08:09:02 pm by tautech »
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Offline mawyatt

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Re: Two Tone Test with Scope and SA
« Reply #39 on: August 01, 2020, 08:08:40 pm »
Agree, this SDS1104X-E looks really good even slightly better performance than the SDS2104X!! Amazing considering the price!!

Best,
Research is like a treasure hunt, you don't know where to look or what you'll find!
~Mike
 

Offline tautech

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Re: Two Tone Test with Scope and SA
« Reply #40 on: August 01, 2020, 08:21:35 pm »
Agree, this SDS1104X-E looks really good even slightly better performance than the SDS2104X!! Amazing considering the price!!

Best,
Siglent's do like a lot of waveforms displayed for FFT so the limits with low frequencies are at a firm 50ms/div when anything slower drops into Auto Roll mode.
FFT Horizontal menu settings (Hz/div, Span) are also limited by timebase settings in SDS1104X-E so some small juggling act ensues to obtain best settings. Practice makes perfect.  ;)

Maybe I'll do a comparison between a few models at just one frequency squeezing the best I can outta each model.
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Offline mawyatt

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Re: Two Tone Test with Scope and SA
« Reply #41 on: August 01, 2020, 08:24:51 pm »
The $499 SDS1104X-E.......
...............

That looks good!
They're as good as you drive them.  ;)

Rejected for posting as I didn't take enough time with the settings and particularly not a slow enough timebase:
Compare with last above.



The $379 SDS1202X-E will be next....when I get a chance.

Rob,

The 1 and 4 markers should be on the two small tones on each side of the larger tones, they are spaced the delta frequency of the larger tones on each side. Since the two large tones are at 10.00MHz and 10.01MHz, delta F is then 0.01MHz (10KHz), then the 3rd Order IMD products are at 9.99MHz (2F1 -F2) and 10.01MHz (2F2-F1). This looks like these 3rd Order IMD products are over 65dB down (don't know how you squeeze this from an 8 bit converter, but your result show such!!), which is quite good indeed :-+

Nice work :clap:

BTW can these results be brought into an app for a better resolution FFT display?

Best,
« Last Edit: August 01, 2020, 08:31:43 pm by mawyatt »
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Offline tautech

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Re: Two Tone Test with Scope and SA
« Reply #42 on: August 01, 2020, 08:46:39 pm »
Rob,

The 1 and 4 markers should be on the two small tones on each side of the larger tones, they are spaced the delta frequency of the larger tones on each side. Since the two large tones are at 10.00MHz and 10.01MHz, delta F is then 0.01MHz (10KHz), then the 3rd Order IMD products are at 9.99MHz (2F1 -F2) and 10.01MHz (2F2-F1). This looks like these 3rd Order IMD products are over 65dB down (don't know how you squeeze this from an 8 bit converter, but your result show such!!), which is quite good indeed :-+

Nice work :clap:
FYI nothing special was done with Markers in these shots other than select Peak which is why they are where they are.  ;)
We can select Frequency which will place them on the nearer tones or manually position them and select how many markers we wish to display.
To date I've just let the Markers do their thing with just a Peak setting.
This ^ applies to all Siglent models shown thus far.

Quote
BTW can these results be brought into an app for a better resolution FFT display?
Probably but beyond my pay grade and understanding. Most stuff can be exported as a CSV Save.

We can however instead of using Split screen FFT use an Exclusive FFT mode and maybe I need drop a couple of shots in to show how different it looks.
With models shown thus far we can also port to any size display we like using the Webserver feature via a LAN link to a PC.
The LAN speeds on these are pretty quick however there is a wee latency when porting to another device.
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Offline mawyatt

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Re: Two Tone Test with Scope and SA
« Reply #43 on: August 01, 2020, 09:59:43 pm »
Rob,

The 1 and 4 markers should be on the two small tones on each side of the larger tones, they are spaced the delta frequency of the larger tones on each side. Since the two large tones are at 10.00MHz and 10.01MHz, delta F is then 0.01MHz (10KHz), then the 3rd Order IMD products are at 9.99MHz (2F1 -F2) and 10.01MHz (2F2-F1). This looks like these 3rd Order IMD products are over 65dB down (don't know how you squeeze this from an 8 bit converter, but your result show such!!), which is quite good indeed :-+

Nice work :clap:
FYI nothing special was done with Markers in these shots other than select Peak which is why they are where they are.  ;)
We can select Frequency which will place them on the nearer tones or manually position them and select how many markers we wish to display.
To date I've just let the Markers do their thing with just a Peak setting.
This ^ applies to all Siglent models shown thus far.


On most systems the closer small 3rd Order IMD tones are more dominate than the ones father out as things begin to roll off as you move away from the dominate 2 tones. This appears to be a little different, either case it's really good performance!!

Yes, a single screen image of the FFT would show better. The TD display doesn't shown much as we've seen (all look almost exactly alike) and why this 2 tone test shows more on what's going on within the scope under test regarding DR.

I'm already sold but others may benefit form this.

Best,
Research is like a treasure hunt, you don't know where to look or what you'll find!
~Mike
 

Offline tautech

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Re: Two Tone Test with Scope and SA
« Reply #44 on: August 02, 2020, 12:01:37 am »
Rob,

The 1 and 4 markers should be on the two small tones on each side of the larger tones, they are spaced the delta frequency of the larger tones on each side. Since the two large tones are at 10.00MHz and 10.01MHz, delta F is then 0.01MHz (10KHz), then the 3rd Order IMD products are at 9.99MHz (2F1 -F2) and 10.01MHz (2F2-F1). This looks like these 3rd Order IMD products are over 65dB down (don't know how you squeeze this from an 8 bit converter, but your result show such!!), which is quite good indeed :-+

Nice work :clap:
FYI nothing special was done with Markers in these shots other than select Peak which is why they are where they are.  ;)
We can select Frequency which will place them on the nearer tones or manually position them and select how many markers we wish to display.
To date I've just let the Markers do their thing with just a Peak setting.
This ^ applies to all Siglent models shown thus far.


On most systems the closer small 3rd Order IMD tones are more dominate than the ones father out as things begin to roll off as you move away from the dominate 2 tones. This appears to be a little different, either case it's really good performance!!

Yes, a single screen image of the FFT would show better. The TD display doesn't shown much as we've seen (all look almost exactly alike) and why this 2 tone test shows more on what's going on within the scope under test regarding DR.

I'm already sold but others may benefit form this.

Best,
Another point of reference when you asked about better resolution.
Well of course if we know the fundamentals are where they should be we can go chasing more resolution with a different Ref position and increased vertical scaling.
Here I've selected a full screen display that still shows the source waveform yet if that's not required we can select exclusive FFT, neither of which are hamstrung for resolution like the SDS1104X-E 50/50 split display.

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Offline mawyatt

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Re: Two Tone Test with Scope and SA
« Reply #45 on: August 02, 2020, 12:32:55 am »
That's a nice result and display.

I'm sold, are discount coupons available for the SDS1104X-E & SDG1032X?

Thanks,

Best,
« Last Edit: August 02, 2020, 12:52:30 am by mawyatt »
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Offline tautech

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Re: Two Tone Test with Scope and SA
« Reply #46 on: August 02, 2020, 01:51:37 am »
Here's another shot from SDS2104X Plus diving deeper towards the noise floor in full screen FFT mode.

« Last Edit: August 02, 2020, 01:53:27 am by tautech »
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Offline bicycleguy

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Re: Two Tone Test with Scope and SA
« Reply #47 on: August 02, 2020, 05:02:18 am »
Since you seem to be comparing FFT implementations wouldn't it be better to ask for something that can be compared like:
What are the closest 2 tones that can be separated with 3dB of dip between peeks and what's the highest and lowest frequency they can be done at.
Unfortunately the limits are set by the weakest link in the tone generator or the scope.

With Siglent SDG2042x and Keysight DSOX2014A, both enhanced.

Example: 119.99MHz and 120MHz high freq. limited by SDG and resolution by DSO FFT


Example 10 Hz and 10.05 Hz  and low, resolution limited by taking too much time to scan  :=\
« Last Edit: August 02, 2020, 05:59:28 am by bicycleguy »
 

Offline PeDre

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Re: Two Tone Test with Scope and SA
« Reply #48 on: August 02, 2020, 09:15:30 am »
A new attempt with the Rigol DS1104Z, this time it worked better with 1 MHz and 1.01 MHz tone.
But no comparison with tautech's SDS1104X-E.
 

Offline tautech

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Re: Two Tone Test with Scope and SA
« Reply #49 on: August 02, 2020, 09:19:15 am »
A new attempt with the Rigol DS1104Z, this time it worked better with 1 MHz and 1.01 MHz tone.
But no comparison with tautech's SDS1104X-E.
Try a faster timebase as AFAIK Rigols FFT works better with lesser waveforms on the display.
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