/diy/ - Do It Yourself

>>1351271
do you understand how an AM receiver works? a tuned circuit resonates with energy coupled in from an antenna, and the amplitude of the voltage across the tuned circuit is turned into a dc output that follows the amplitude of the signal and therefore approximates the audio signal. this is covered in most explanations of "boy scout" crystal radio sets
in the real world, tuned circuits aren't perfect and they'll still resonate with frequencies either side of the center frequency, to a lesser degree the further away (this is quantified as "quality factor" aka Q). assuming an otherwise clear band (which, in the real world, would be taken care of by additional band pass arrangements ahead of this section), if you tune the circuit's fO to the top end of the FM channel or just above, such that the FM channel falls within the sloped part of the curve around fL on Pic related, the higher the received frequency imposed upon the tuned circuit, the higher the amplitude of the signal on the tuned circuit, and from there you can use a plain old AM detector to get audio
you should probably start with basic ac circuit analysis, or maybe some study material for the FCC technician class ham license will cover it. /ohm/'s OP has some good resources for babby's first electronics