"The IF signal has a phase that is the difference between transmit and received signal phases."
Yes. That's a neat property of superhetrodyning - phase is preserved. Both the outgoing and incoming signals are down-converted by mixing with the local oscillator. The phase angle difference between out and in is the same at both the transmitted/received frequency and the IF frequency. But down at the IF frequency, you get to work at a lower frequency where it's easier to do A/D conversion and counting. Most software defined radios still have a superhetrodyne front end, so the digital stuff is working at the IF frequency.
This is less necessary than it used to be, now that digital circuits can work well into gigahertz ranges.
Heh, when getting a GPS Disciplined Oscillator set up I was feeding the 10 MHz oscillator into an SDR to use as a reference clock and was calibrating against a local cell tower. 7 Hz beat/offset at 1700 MHz!
Yes. That's a neat property of superhetrodyning - phase is preserved. Both the outgoing and incoming signals are down-converted by mixing with the local oscillator. The phase angle difference between out and in is the same at both the transmitted/received frequency and the IF frequency. But down at the IF frequency, you get to work at a lower frequency where it's easier to do A/D conversion and counting. Most software defined radios still have a superhetrodyne front end, so the digital stuff is working at the IF frequency.
This is less necessary than it used to be, now that digital circuits can work well into gigahertz ranges.