I believe someone said that the coils are not absolutely necessary but an improvement, so we could drop all the GD348 and mixer circuit, and it should still "work". That would let us with a simple passive receiver, so this must be the heart of the circuit.
Apparently the idea when tuning it is to cancel any magnetic reaction, so we end up with a receiver that detect only RF levels variations...
mmmh...No wonder it is somewhat erratic and depends on geography ...
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