FM Demodulation

498

04:29:56

Okay i tried, but this is in no way a viable circuit. In reality making it will fail miserably. 

How it works: I'm not going to get into the modulator part. It's just a VCO 555 timer well above its maximum operating frequency. The Demodulation works something like this. First you apply the modulated signal through a specifically chosen LC filter with a given Q factor. As the FM deviates in and out of the LC filter's center frequency the frequency shift gets converted into an amplitude shift. This means that the FM must first be converted to AM before any further demodulation. Then it's a simple matter of envelope detection (the diode and everything to the right of it). Here's a youtube link of an army training film that explains it in detail.  https://youtu.be/xn6lzrMJUDs and another one https://youtu.be/gfz1FbIOMbs 

published 9 years ago

WTFCircuit

9 years ago

At least it works... Almost...

Karma247

9 years ago

Looks good

thebugger

9 years ago

It works, almost indeed. The carier/modulator frequencies are too close, and the filtering is not so effective, but it's only exemplary

jason9

9 years ago

Thank you so much. However, it doesn't really work. I got the basic idea though. :D

jason9

9 years ago

Well, it sort of works.

WTFCircuit

9 years ago

If I has a 20-40pF adjustable capacitor (I'm not sure about the values because I don't have a multimeter that precise) what coil should I use to receve a FM signal?

thebugger

9 years ago

Something in the range of 70-100nH. An 80nH coil with a 32pF capacitance will resonate at 100Mhz. The impedance of the tank circuit will be 50ohm. To construct an 80nH coil you'll need to wind an inductor with these parameters. 6 turns over a 5mm diameter (air core) evenly spaced at a 10mm height. I hope this helps.

WTFCircuit

9 years ago

Yes, thanks a lot!

jason9

9 years ago

Hey, I posted a comment on your "Ultimate Hi-Fi Class B Amplifier V3.2".

add comment in editor

EveryCircuit is an easy to use, highly interactive circuit simulator and schematic capture tool. Real-time circuit simulation, interactivity, and dynamic visualization make it a must have application for professionals and academia. EveryCircuit user community has collaboratively created the largest searchable library of circuit designs. EveryCircuit app runs online in popular browsers and on mobile phones and tablets, enabling you to capture design ideas and learn electronics on the go.