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This is probably a basic question but I didn't find any answer online.

Suppose we configure a SDR (least say, with a maximum sample rate of 100 Msamples/s) with a low sample rate (e.g. 1 Msample/s).

  • Does the SDR actually samples at 1Msample/s and sends only that (e.g. to GNU-radio)?
  • Or does the SDR sample at 100Msamples/s and decimates and then sends the decimated 1Msample/s?
  • Or does this depend on the SDR? If this is the case, are there examples of SDRs that do the 1st or 2nd option

Thank you in advance!

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If the SDR and ADC is designed to sample at 100 MHz, then the analog anti-alias filter of properly designed is also wide enough for most of that bandwidth up to Nyquist (or could use bandpass sampling to undersample a higher frequency band with a bandwidth at 85% of Nyquist or so).

That said, we would never want to configure the SDR to sample at 1 Ms/sec due to the significant noise elevation and interference due to aliasing. The OP is correct in the desire to sample at the highest rate and then decimate digitally to a lower rate.

This will be specific hardware and software capabilities (as to what the user can configure ) for the given SDR design. I recommend reading the manufacturers datasheet and contacting them about such possible configurations. There is nothing about a generic “SDR implementation” that would preclude the ability to do this, but the initial point I made about ensuring the signal is sampled at the rate consistent with the analog anti-alias filter would always hold (unless you want to make such hardware changes to the board).

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