Hi, I'm currently working on a plug-in squelch solution for radios that do not have a squelch function themselves, such as many of my Tecsun radios. Looking at many of the circuit designs freely available, I have yet to find one that satisfies one of two conditions:
1) Completely passive, requires no power supply whatsoever, besides the 3.5mm input. (Maybe this is a ridiculous notion. Please tell me if it is.)
2) Swaps out its transistors for something more feasible like Diode Resistor logic, making it more suited for low power operation.
Thanks!