Specializing the FM transmitter

Discussion in 'General Electronics Chat' started by crazybuoy, May 18, 2012.

  1. crazybuoy

    Thread Starter Active Member

    Sep 19, 2010
    I want to build a small FM transmitter but want that only my FM receiver could catch my transmitter. To do this, I think I also have to make some changes in FM receiver (that is normally available in market).

    Please guide me what are the main things I have to change or do in FM transmitter and receiver.

  2. Audioguru


    Dec 20, 2007
    Do you want to modify a normal FM radio so it receives a frequency that is not normal?
    Then do the same modification to a simple poor performance transmitter?
    It is a lot of trouble and since most frequencies are used by communications and aircraft then you might cause serious interference to them then you can be jailed (or shot or hanged or all three).

    What about using one of the many methods of encryption?
    I installed and modified boardroom tele-conferencing systems for a few years. An insurance company built a new building and wanted a wireless boardroom tele-conference system that could not be heard by the neighbours. I built a single-sideband transmitter for the FM broadcast band and a decoding receiver for it. They worked perfectly since normal FM radios received gibberish and my decoded receiver sounded perfect.
    Then the insurance company was charged with cheating the market and went bankrupt.
    No wonder they didn't want anybody to hear their cheating secrets.
    PackratKing likes this.
  3. PackratKing

    Well-Known Member

    Jul 13, 2008
    Curiosity Guru..........will this system you describe also work to "isolate" an RC vehicle from the other 20 million controllers out there ???
  4. dataman19


    Dec 26, 2009
    Incidentally, make sure you are going down in frequency.
    Most airports use localizers that are in the 108-109 MHz Range - this is a "Toboo" and "Forbidden Range" for any transmitter to operate. It is strongly suggested that you include a 107.9MHz to 109.7MHz band stop filter.
    Phoenix, AZ
    PackratKing likes this.