In answer to : http://everycircuit.com/circuit/6039273503981568 bottom section is the analog (100Hz AC signal) FM ......frequency modulated 1.47kHz carrier of the 555. Above is my effort at a Foster Seeley FM demodulator. It needs a little tweaking. I'm open to criticism with it....hopefully not unkind! The red trace output settles around the required 100Hz as a copy of the original signal. (at least...that is the idea). The transistor on the 555 was necessary, since attaching the modulated wave to the demodulator did itself alter that initial carrier wave here on EC when taken there directly from pin3.
(unwanted AM signals can be a problem with this type of demodulator)
