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FFT - Rohde & Schwarz RTB2002 vs. Siglent SDS2104X Plus

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Hardware:
I had the opportunity to see a Rohde & Schwarz RTB2002 70MHz and a Siglent SDS2104X Plus. I am looking for a replacement for my 30 years old Hameg HM412-5.
For this I took a look at the sine and square wave signal of my new SGS2042X.
So I am still inexperienced with the DSOs.
That the measurement results were not always so identical is probably due to the tolerances.
Now I have also looked at the FFT function and compared it. Of course I know that the built in spectrum analyzer is only a little bit comparable to a real spectrum analyzer.
But the difference between the R&S and the Siglent was so big that it is not clear to me what the cause is.
Regarding the shown levels in dBm and the spectrum I see serious differences.
Yes, I have one oscilloscope on one channel and the other oscilloscope on the other channel. But I also changed the channels but it did not lead to a fundamental change of the displayed problem.

Did I do something wrong or do I expect too much?

The first two pictures show the FFT of a 1kHz sine wave.
The second two pictures show the FFT of a 100kHz square wave signal.


2N3055:
Did you put external  50 Ohm terminator on R&S for measurements?
It doesn't have built in 50 OHm termination.
Also you should try to make both measure with similar RBW and same FFT Window..

Hardware:
Yes, I had a 50Ohm resistor on the R&S. Regarding the FFT window the settings are identical or nearly identical. You should be able to see that in the pictures.

Fgrir:
For 1KHz you are comparing dBm and dBV, you should expect to see different results.

For both frequencies on the Siglent you have C2 off the top of the scale, are you sure you aren't clipping the waveform?

Andreas:

--- Quote from: Hardware on September 18, 2020, 02:28:56 pm ---
Did I do something wrong or do I expect too much?


--- End quote ---
I fear you have a signal clipping on the Siglent (50mV/Div versus 200mV/Div)

with best regards

Andreas

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