One way or an other...
When the PIC senses that the signal has been lost (or getting bad) it could try to tune up a certain number of steps, if that didn't work it tunes down instead. The signal must be somewhere, or it just sweps the entire band for a signal.
Probably will the FQ drift mostly in one direction and then we start tuning that way.
Feeding the AGC point into an AD converter in the PIC would be neat but it requires som reverse engineering to find it.
A proper filtered HPWM should have a nice DC level out but as you say, a resistor network from the I/O will do just as fine.
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