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SA video bandwidth affects signal level?
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Richard Head:
The TG and SA need to track properly in order for the amplitude to be correct. At narrow RBW settings (<100Hz) it gets quite critical as a very small freq error between the TG and SA receiver can cause the TG output to fall outside (or on the filter skirt of) the IF filter passband. The calibration procedure just requires a coax between the TG and the SA input and when the cal button is pressed the instrument will align the two so the trace is level. This is normally only necessary when very narrow RBW's are used such as when checking the response of crystal filters. The newer SA's probably do it automatically now.
jonpaul:
I cannot testify on the R&S, or,modern FFT SA.

A TG is not a,good test, instead use a single tone, with any traditional swept /LO/mixer/IF analog SA, eg Tektronix 7L5, 7L12, 7L13 or HP 4195A, HP8558B, etc.

change sweep speed with no video,filter observations of shape of tone displayed and level at center.

As,sweep speed is increased, at some,point level at peak decreases and shape is distorted and asymmetrical

The relationship between sweep speed, RBW, sweeping width of a SA is very well documented
See the already mentioned Tektronix Circuits Concept book Spectrum Analyzers.

In Signal processing, the same limitations must apply to FFT Analyzers.

With Kind Regards

Jon
jmw:

--- Quote from: Richard Head on March 24, 2023, 12:34:47 pm ---The TG and SA need to track properly in order for the amplitude to be correct. At narrow RBW settings (<100Hz) it gets quite critical as a very small freq error between the TG and SA receiver can cause the TG output to fall outside (or on the filter skirt of) the IF filter passband.

--- End quote ---
This could explain why the FPC constrains the RBW to a minimum of 1 kHz when using the tracking generator.
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