AM Radio Transmitter using a Tuner/Variable Capacitor

Discussion in 'The Projects Forum' started by don3194, Jan 17, 2016.

  1. don3194

    Thread Starter New Member

    Jan 17, 2016
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    I just finished repairing an old radio from the 40s, and I was wondering if I could build an AM Transmitter using a Tuner/Variable capacitor. If not, I will just build a transmitter from a Crystal Oscillator.
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,539
    1,251
    Assuming the radio is a heterodyne or super-het design, there is a local oscillator. But you would have to add a modulation scheme, and the LO is tuned 455 kHz away from the broadcast band.

    ak
     
  3. don3194

    Thread Starter New Member

    Jan 17, 2016
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    0
    I am not that great in electronics, how would I figure out if it is a heterodyne or a super-heterodyne? What is the "LO" and what is a modulation scheme? I must sound stupid, but if you don't know just ask.
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
    745
    your 1940s AM set is probably valve, and will be a hetrodyne receiver, the front end tuner is mixed with a local oscillator (LO) which is usually 470Khz higher than the tuner, this produces a mixed signal of both the sum and difference, the difference is 470Khz and this is amplified and demodulated by the diode to produce an am signal.

    https://web.archive.org/web/2015010...om/circuits/mw_transmitter/mw_transmitter.htm
     
    Last edited: Jan 18, 2016
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