I'm trying to build an FM receiver (and eventually transmitter) in GnuRadio that will be able to interact with my local repeater. Starting with WBFM (because I can consistently pull in broadcast stations for testing) I created 3 receivers:

  • Directly tuning my SDR hardware to the station I want to listen to
  • Tuning the hardware to some base frequency, then multiplying by a cosine; heterodyne
  • Tuning the hardware to some base frequency, then using the Frequency Xlating FIR Filter

My question is, which is the better method given I eventually want narrow-band FM with split transmit & receive against a repeater?

I'm guessing having to change the hardware's frequency from receive to transmit, then back again will be "too slow". I'd think that going back-and-forth between cosine sources wouldn't be too bad, but I'm wondering if there is an advantage to the Frequency Xlating FIR Filter. Thoughts or advice? Thanks!


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