Sorry for the longish post. I have a receiver using an RPi4 & an RTL-SDR dongle that outputs audio via the analogue jack- I'd like a low cost solution. I need the time delay through the system to be constant & the 2-clock problem means it won't be.
I can make the phase difference between transmitter modulating signal & the SDR audio output & make it increase or decrease over time by adjusting the Frequency Offset of the Osmocom source. I'm not sure exactly what this is doing but seems to tweek the sample clock. Anyone have any info on this?
If there is a way to get access to the ALSA buffer pointers using a Python OOT block? Then I may be able to work on the average difference to adjust the Osmocom frequency offset to get a constant phase. It would be interesting to try but ultimately, I will probably need to hold the delay more precisely. But, the control loop can be slow as the drift is very slow.
A hardware solution could be to create a clock for the RTL-SDR that's locked to the RPi clock. Anyone attempted anything like this or have any comments on the viability. I would assume all clocks on the RPI are generated from the 19.2MHz crystal; the audio 48kHz is 1/400 of this so I'd hope it was locked.
Thanks for the help, Dave