How to Effectively Prevent Aliasing When Using Low Sample Rates with KrakenSDR?

1

Hi everyone,
I’m using KrakenSDR for multi-channel IQ data acquisition and I have a question regarding aliasing when using low sample rates.
When I set the sample rate to 500 kHz, I notice that strong signals outside the ±250 kHz bandwidth still appear at the edges of the spectrum display, which I believe is due to aliasing. I understand that digital (software) filters in GNU Radio can help clean up the signal after digitization, but they cannot remove aliased signals that have already folded into the band during ADC.
My questions are:

  1. Does KrakenSDR have any built-in analog anti-aliasing filters that track the configured sample rate, or is it necessary to add external analog filters before the SDR inputs?
  2. What are the recommended practices for preventing aliasing when using low sample rates with KrakenSDR?
  3. Are there any recommended external filter products or design guidelines for this use case?
  4. Is there any way to configure the hardware or firmware to help mitigate this issue?
    Any advice or experience from the community would be greatly appreciated!
    Thank you!
2

KrakenSDR with based on R820T2 RTL-SDR dongles, and the R820T2 does have antialiasing filters in it, but they are less effective at lower sample rates.

Best practice is generally to sample as high as possible, then use FIR decimation to get down to the signal you want.