Quadrature FM Demodulation

256

01:47:13

Changing frequency will result in proportional change in Red current level.
Wait for a while for red line to be stable!!!!

The AND gate output is dependent upon the phase difference between the two signals, i.e. it acts as a phase detector and produces a voltage output that is proportional to the phase difference and hence to the level of deviation on the signal.

http://www.radio-electronics.com/info/rf-technology-design/fm-reception/fm-quadrature-detector-demodulator.php

With Better Modulation Index. Changing the frequency will increase or decrease the max peaks at the output of and gate.
Wait for a minute before you start :p
 Increase in frequency-> higher peaks
Decrease-> Lower peaks.
This way this demodulator can extract info from FM Signals to speaker recognizable format.

published 10 years ago

zorgrian

10 years ago

Very interesting! I remember seeing something like this before but I've never actually built & tested this type of circuit. I worry about the inclusion of 10mV voltage sources and unobtainable 1uOHM resistors CAN YOU EXPLAIN these? Can these unobtainable components be replaced by another circuit configuration? In fact can you provide a circuit explanation - I try to do this despite there being a number of people in this community who provide near insults OR that demand an explanation and then do not comment when I have done so. I would guess that a 'mixer' style demodulation circuit could also be used for FM modulation?

Ashish_kumar_4

10 years ago

Lol the 1u resistor is if no use. Remove it. And add a resistor to 1 v source to obtain 10mv source.

Ashish_kumar_4

10 years ago

The and gate is a mixer in fact

hurz

10 years ago

Ashish, don't forget to filter (lowpass) the mixing products to see the resulting DC voltage, nothing else then DC matters at a baseband demodulator! Spikes are not welcome!

Ashish_kumar_4

10 years ago

Hmm just add a capacitor :3 thats easy.

Ashish_kumar_4

10 years ago

Will do it

hurz

10 years ago

I know, but its your circuit ;)

Ashish_kumar_4

10 years ago

Thanks for your support by the way :)

hurz

10 years ago

You are welcome. Anyway, now you added a filter, unfortunately its not a lowpass its a highpass which will emphasis things we dont want to see and DC is even invisible :-( you need a good lowpass filter. Again, you are welcome.

Ashish_kumar_4

10 years ago

Added. Cant add a better one because it take it longer to be stable and not practical on this app to test this circuit except for real life. Thanks :)

hurz

10 years ago

Yes, if the corner frequency is to low it takes to long within a transient analyse mode of any simulator.

Ashish_kumar_4

10 years ago

Hmm

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