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Zero span spectrum analyzer .FFT, sweep, filters and RBW.
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xugmu:
Hello, I am thinking of buying a spectrum analyzer and the main objective is to see very small signals, RBW between 0.2 Hz and 1 Hz. These resolutions are easily achieved with an SDR and this is where the problem appears: I want to see the signals also in the time domain and here things seem to get a bit complicated.

The SDR works, afaik, in FFT mode and, afaik too, you have to apply a filter to isolate the required bandwidth (in this case zero span which in reality, afaik, would be 0.2 Hz spam, 1 Hz spam or whatever spam, always logically below the SDR bandwidth). A digital 1 Hz filter is difficult to create in my opinion. On the other hand, a sweep spectrum analyzer, afaik, could easily stop the sweep and focus on a point (we would have a bandwidth equivalent to the RBW).

The problem would be buying an analyzer that works in FFT mode and that gives me problems in zero span mode

Best regards
Andree Henkel:
maybe you are actually looking for a "lock in amplifier"?
joeqsmith:
While I know what zero span mode is, I have never heard of "zero spam".  Obviously not a typo.   This is spam but I don't see how it fits into showing time domain signals:

https://www.spam.com/
ftg:
A higher end oscilloscope with good FFT like R&S MXO5.
According to it's datasheet sub-1Hz RBW's seem possible.
xugmu:

--- Quote from: ftg on August 06, 2024, 12:16:31 pm ---A higher end oscilloscope with good FFT like R&S MXO5.
According to it's datasheet sub-1Hz RBW's seem possible.

--- End quote ---

An oscilloscope represents, in the time domain, everything that appears at its input.

What I am suggesting, afaik, is precisely the opposite, to put it in a perhaps not very scientific way, it would be about making a bandpass filter with a bandwidth of 1 Hz and placing it before the oscilloscope.

Best regards
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