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When looking at carrier recovery, a PLL is often applied to correct the frequency offset between the local oscillator and the transmitter after down conversion.

I'm wondering what happens to the PLL if this frequency offset is small? Does the PLL break as the carrier tone isn't as obvious and the loop filter can't as easily differentiate the modulation noise from the carrier?

Wouldn't it be more advantageous to have a local oscillator down-convert the signal to an intermediate frequency and then have the PLL track that?

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  • $\begingroup$ In my experience, what you propose is what is actually done in practice. $\endgroup$ – MBaz Apr 18 '19 at 19:41
  • $\begingroup$ I was reviewing some intuitive arguments for PLL working and for squaring to work(QAM) you need to have your carrier frequency sufficiently high so your signals shifted spectrums don't overlap. So I guess I am right? $\endgroup$ – FourierFlux Apr 19 '19 at 4:10
  • $\begingroup$ Oops I meant BPSK, QAM needs quading $\endgroup$ – FourierFlux Apr 19 '19 at 4:41

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