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FSK demodulation

  1. Sep 17, 2014 #1
    I have a transmitter(ADF7021-N) that I've programmed to transmit data at 145Mhz. I wanted to verify whether my code is right or not. however due to the unavailability of a receiver or radio, I decided to check my code using an oscilloscope, but received no concrete results. Is my concept viable or are there other ways to test this code?
  2. jcsd
  3. Sep 18, 2014 #2


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    Staff: Mentor

    Hi kshitij14395. I see you are new hereabouts. http://imageshack.com/a/img515/4884/welcomesign.gif [Broken]

    Are you saying you have a carrier that basically jumps around among 4 or 5 known frequencies? What is the lowest and the highest of these frequencies it will have?
    Last edited by a moderator: May 6, 2017
  4. Sep 18, 2014 #3


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    Staff: Mentor

    Welcome to the PF.

    Do be a bit careful when testing your transmitter. What band is 145MHz in your country? You need to be sure not to create interference with other licensed radios in your area. So testing with only a coax cable from your transmitter into the 50 Ohm termination of your oscilloscope is probably a good idea.

    What oscilloscope do you have? Can it do FFTs? Can you store part of the waveform and export it as a file to run an FFT on with your PC?
  5. Sep 18, 2014 #4
    First, I would agree that you need to check your licensing...145 MHz is in the middle of the 2-meter amateur band in the U.S. As long as you don't actually transmit (such as using a dummy load) that wouldn't be a problem....but be safe.

    The simplest FSK demodulator is "slope detection", or what i like to call "slop" detection. Use a sharply tuned filter tuned slightly off center from the unmodulated carrier. As you modulate the carrier, you should see a change in the amplitude. Look up "discriminator" on the web for more details.

    When you're ready to polish your circuit, you'll probably want to use some kind of PLL for decoding.

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