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Trying to display bandwith via Math on Siglent SDS2k+/2kHD/800X HD
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Martin72:
Hi all,

As mentioned (and suggested by 2N3055) in the Siglent SDS2000X plus thread, I´m starting a dedicated one for this "problem".
Actually in questionmarks because it´s not really clear if this is a problem sitting in front of the scope... ;)
What was happen ?
In the siglent thread the question came up if you can´t display the bandwith (frequency response) by using the math functions.
You can:

https://www.eevblog.com/forum/testgear/siglent-sds2000x-plus-coming/msg4156720/#msg4156720

I´ve tried to reproduce it on my sds2504x+ but it failed somehow:

https://www.eevblog.com/forum/testgear/siglent-sds2000x-plus-coming/msg4157086/#msg4157086

Then 2N3055 took another scope from siglent, it works.
And so on, and so on, see the following posts there.
The expression used in the first time by 2N3055 is FFT(d(Channel)/dx).

At work I checked this with three different scopes from lecroy.
-Waverunner 9054, 500Mhz, 20GSa/s
-HDO6034A, 350Mhz, 10GSa/s
-Wavesurfer WS3024Z, 200Mhz, 4GSa/s

On all the models you can´t do very much on the FFT adjustments(like memorypoints, markers and so on the siglent got).
Max. resolution was 10ns/div, above (5ns and more) the ws3024z didn´t display the function proper(No problem for the Waverunner)
Today I used the same settings at home on my siglent for comparison all the scopes directly.
Tomorrow I´ll follow the questions/suggestions from gf:


--- Quote ---- FFT(d(Intrp(C1))/dt)
- 20x interpolation
- dx as short as possible
- Flat Top window function
- span 0...1GHz
- 2µs/div (as before) might be a reasonable starting point.
--- End quote ---

https://www.eevblog.com/forum/testgear/siglent-sds2000x-plus-coming/msg4171216/#msg4171216

Goal of this new thread is to find out, if this is a bug to fix or if this siglent model is simply not capable to do this.
Or it´s me who is not capable to do this...  8)
The last is no problem, I´m always willing to learn.
EDIT : Title changed.
Martin72:
Pics from the "big" scopes..
rf-loop:
I do not have same kind of signal available now.
But because these are just partially for fun, I use SDS1104X-E oscilloscope Trig out for get edge what is still possible to measure with this scope, so it is suitable signal for this scope when it works 2GSa/s real samplerate. (if use 1GSa/s this signal rise is too fast). This all is not meaningful at all in this case.

But then this what was @gf ask (originally in other thred)


--- Quote from: gf ---- FFT(d(Intrp(C1))/dt)
- 20x interpolation
- dx as short as possible
- Flat Top window function
...
...

--- End quote ---

When I look your images I can not find Interpolation.


Here I have used SDS2504X HD

- FFT(d(Intrp(C1))/dt)
- 20x interpolation
- dx 4 (as short as possible)
- FFT Flat Top window function

1st image (1)a  is 0-2GHz span (iterpolated samplerate 40GSa/s)
2nd image (2)a is full 0-20GHz span (iterpolated samplerate 40GSa/s)
Full span based to real samplerate is of course 0-1GHz

Martin72:
Hi,


--- Quote ---When I look your images I can not find Interpolation.
--- End quote ---

It´s because I didn´t it so far - Until now...


--- Quote ---- FFT(d(Intrp(C1))/dt)
- 20x interpolation
- dx as short as possible
- Flat Top window function
- span 0...1GHz
- 2µs/div (as before) might be a reasonable starting point.
--- End quote ---

Here it is, dx is 4 and can´t be lowered.
I´ve saved all timebases between 2µs and 2ns, here a selection.

gf:


What was the exact math expression here? I just see that it starts with "FFT(Intrp(..."

I think I aked for: FFT(d(Intrp(Cx))/dt).
I.e. interpolate first, then d/dx, and finally FFT.
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