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Bandwidth limit on Siglent SDS2000X Plus oscilloscope
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Performa01:
I use a levelled signal generator (usually Anritsu MG3633A or an AWG like SDG6000X and SDG7000A), slowly sweeping over the desired bandwidth. FFT in peak hold collects the measurements over a few minutes.

This method has proved to be just as accurate and still way faster than manual data acquisition.

The big advantage is that we can tweak it a lot.
We can use very slow sweeps in order to get a nice looking graph right away. We can use a faster sweep so we get a first result pretty quickly, and the let it sweep some more times to fill the gaps in the plot.
What resolution in the frequency domain (RBW) do we need? I've chosen about 920 kHz, (8192 FFT-points @ 2 Gsa/s), but we can alter that if required. More FFT points will slow it down, so we need longer sweep times and/or more sweeps to get a nice contigous plot.
gf:

--- Quote from: Performa01 on August 11, 2023, 01:50:15 pm ---... slowly sweeping over the desired bandwidth. FFT in peak hold ...

--- End quote ---

Thank you, that makes a lot of things clearer.

[ I was errenously assuming that the stimulus was some kind of wide-band pulse fitting into a single FFT window of only 4.096µs, and that would have been quite challenging, with good SNR. ]
Martin72:

--- Quote from: Performa01 on August 11, 2023, 01:50:15 pm ---I use a levelled signal generator (usually Anritsu MG3633A or an AWG like SDG6000X and SDG7000A), slowly sweeping over the desired bandwidth. FFT in peak hold collects the measurements over a few minutes.

--- End quote ---

I had bought an SML01 (1.1Ghz) to recreate this for my 2504X HD.
But I have never done this before, how could a suitable sweep setting for this purpose be parameterized?
500Mhz bandwidth has the scope according to the model name, do you start at 300Mhz and stop at say 800Mhz?
And how could "slow" turn out?
Performa01:

--- Quote from: Martin72 on December 06, 2023, 09:28:27 pm ---
--- Quote from: Performa01 on August 11, 2023, 01:50:15 pm ---I use a levelled signal generator (usually Anritsu MG3633A or an AWG like SDG6000X and SDG7000A), slowly sweeping over the desired bandwidth. FFT in peak hold collects the measurements over a few minutes.

--- End quote ---

I had bought an SML01 (1.1Ghz) to recreate this for my 2504X HD.
But I have never done this before, how could a suitable sweep setting for this purpose be parameterized?
500Mhz bandwidth has the scope according to the model name, do you start at 300Mhz and stop at say 800Mhz?
And how could "slow" turn out?

--- End quote ---
For a frequency response plot from 1 MHz to 1 GHz I use the following setup:

Signal generator
Sweep mode: linear
Sweep time: 300 s
Sweep frequency setting: 1 MHz to 1 GHz
Sweep direction: up
Carrier amplitude: 0 dBm

DSO
Acquisition
Timebase: 500 ns/div
Trigger: edge, 0V, auto - or mains
Input: 50 ohms, 100 mV/div

FFT
Max points: 8 kpts
Window: Flattop
FFT mode: Max-Hold
Vertical: 2 dB/div, Ref = +2 dBm, Unit dBm, Ext. Load = 50 ohm
Horizontal: 0 - 1 GHz

The trace might not be perfect after the first pass, but you can just wait and let consecutive passes accumulate to get an optically nice result.

See attached example.

SDS2504X HD_FR_Full_0dBm_split

Of course you can choose a different frequency range, but this doesn't make much sense, because we always want to see the level at low frequencies as a reference. Usually, we take 1 MHz as reference and with the settings given above, this is just possible, because the RBW is still below 1 MHz. For faster scans we need to use wider RBW (= less FFT points) and then we also need to switch to 10 MHz as the reference frequency.
Martin72:
Thank you very much  :-+
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