I need to demodulate an FM signal (4 MHz max deviation) with a strong center frequency drift (550-800 MHz). I've built an AFC circuit to track the drift and now I need to build a tunable quadrature detector to demodulate the signal itself and I'm having trouble making it tunable since the Q of RLC network (C18, R12, L5) will change if I change the capacitance to adjust the center frequency and I need to compensate this Q change somehow.
Here's a schematic with limiting amplifier (left), wideband quadrature detector for AFC (center) and tunable quadrature FM detector (right).
UPD1: I'm thinking towards electrically controlled inductors because Q change is small enough if L is adjusted instead of C but I don't see any of those commercially available.
UPD2: I looked in the datasheet of the inductor I'm using and noticed that its Q factor increases with frequency and I think it should compensate tank Q reduction with frequency.