How does a comparator look inside/ can an opposing voltage source act as a resistor

Discussion in 'General Electronics Chat' started by Msaf1123, May 23, 2016.

  1. Msaf1123

    Thread Starter New Member

    Mar 25, 2016
    Right now I'm trying to use an inverted ac voltage source to cancel out a fm carrier wave an leave me with the modulated signal. Would that work or am I just wasting my time?
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
    Please post a schematic of your circuit, and a much bettter descirption of what your inputs are, voltage, frequency, etc.
  3. MrAl

    Distinguished Member

    Jun 17, 2014

    First, the inverted wave would have to be in perfect phase relation to the carrier.
    Second, if the FM varied from 100kHz to 120kHz, you'd be left with a wave that varies from 0 to 20kHz, or -10kHz to +10kHz. We could look into this more though, it may not even be that good :) It probably has to be 'mixed'.
    When i do the subtraction sin(w1*t)-sin(w2*t) with f1=12 and f2=10 i get f2 modulated as 'bursts" which look like the beat frequency times 2. Full wave rectified they look like modulated half sines, so they would have to be filtered and every other one inverted or something like that to recover the beat frequency.

    You might want to look into known methods of demodulating FM signals. It's much harder to do than demodulating AM signal.
    Sometimes a constant frequency is mixed with the input to get a lower mid range frequency to work with too.
    Last edited: May 23, 2016