Electronics > RF, Microwave, Ham Radio

Does professional spectrum analyzer such as keysight,RS has `aliasing` problem?

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youta556:
When play SDR equipment,I always change 'sample rate' to avoid `aliasing` problem. 
When I using professional spectrum analyzer,such as keysight n9030a,Should I change 'sample rate' to avoid `aliasing` problem?

bob91343:
Aliasing is more often an oscilloscope problem.  A spectrum analyzer calls it the way it sees it.

Marsupilami:
Probably not, but I'm sure it depends on the actual instrument.
In case of such signal analyzers as the 9030 in fft mode those implement an adequate analog IF filter for the maximum sampling rate (or maybe for a couple of lower rates too). That gets rid of the aliasing products during A to D conversion. The bandwidth shown on the screen is further downsampled digitally, again with appropriate digital filtering. This is not particularly complicated but processing intensive especially for high sampling rates, thus lower cost equipment might exclude it and put the burden on the operator to deal with aliasing.
Again I'm not sure but if I had to guess for the n9030a the relevant spec in the datasheet is:

Residues, images, and spurious responses: –100 dBm nominal

Traditional swept spectrum analyzers don't suffer from this issue at all.

HTH

tggzzz:

--- Quote from: bob91343 on May 19, 2022, 11:35:07 pm ---Aliasing is more often an oscilloscope problem.  A spectrum analyzer calls it the way it sees it.

--- End quote ---

You should play with spectrum analysers that don't have a preselector. They usually have a button that helps you visually distinguish signals from aliases.

Tek an HP scopes tended to have optional preselectors, to reduce the cost where they aren't necessary.

TheUnnamedNewbie:
With the default input, no, I don't think it's common. But with external mixers, it can happen. But then I don't know if you would call it aliasing, it's more a combination of upper vs lower sidebands, and the fact that harmonic mixers mix with all harmonics, and not just the one you really want to measure.

They have some clever tricks to deal with it (like wiggeling the LO a bit, and if you, say, use a 10th harmonic, you expect tones to wiggle 10x that amount. Suppress anything that wiggles a different amount). They all give it fancy names, like Signal ID and so on

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