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Resolution bandwidth of a spectrum analyzer

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neazoi

neazoi

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hello,
does the resolution bandwidth of a spectrum analyzer defined primarily by the bandwidth of the IF amplifier? (assuming only one IF amplifier)

I have already read HPs spectrum analyzer basics, I just want to make sure practically, that if I change the filter before the amplifier on an old spectrum analyzer, then I could get higher resolution out of it.
 

If you particularly want to increase the resolution, several parameters have to fit as well, e.g. scan speed, oscillator accuracy and phase noise, video filter bandwidth.
 

You can think that a Spectrum Analyzer is a superheterodine receiver (with one, or multiple IF conversions), where the RBW is given by the bandwidth of the IF filters.
Video Bandwidth is given by the bandwidth of the filters placed after the detector.
 

So it should be enough to minimize the IF filter bandwidth in order to achieve better resolution? (assumming only one IF)
 

If the scan speed can be set sufficient low and the oscillator accuracy doesn't thwart the resolution enhancement. Factor 2 or 5 should be feasible anyway.
 

The scan speed has to be slower to allow for the setting of the filter, also the phase noise of the local oscillators must be good to avoid that the LO frequency will fall outside the IF bandwidth and also the video speed can be lower to reduce the post detector noise.
In this cas eyou can have better sensitivity, otherwise you will see the level of your signal decrease without any reason.
Take a lot of care about of the LO noise, especially if you want to modify an existing spectrum analyzer; this is the most difficult parameter to respect.

Mandi
 

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