AM modulation using MOSFET

Discussion in 'Wireless & RF Design' started by kadotettu, May 16, 2009.

  1. kadotettu

    Thread Starter New Member

    May 14, 2009
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    I am making a small AM Transmitter for short wave band. It needs to transmit voice from a tape player with a range of about 20 meters. I thought the easiest way to modulate the signal would be to use an op-amp to combine the carrier and audio input, but since I don't have any and the nearest electronics shop is far away I decided to combine the signals just by joining the wires and use a power mosfet to amplify it. I know a little about electronics and know this might be a stupid guestion, but could someone verify if this should work. The crude picture attached should clarify what I mean.

    Any help will be appreciated
    Thanks
     
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  2. bertus

    Administrator

    Apr 5, 2008
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  3. kadotettu

    Thread Starter New Member

    May 14, 2009
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    Thanks Bertus!

    I spent time reading more about modulation techniques from the link you provided. Then I modified my circuit and now it seems to work just fine. Now it first creates and amplifies the carrier wave and then modulates using normal bipolar transistors.
     
  4. DickCappels

    Moderator

    Aug 21, 2008
    2,656
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    This is my favorite AM transmitter. Adjust the inductors to your application. You can capacitively couple your carrier into the base of the left-most transistor in place of the crystal.

    This should allow good, clean, amplitude modulation. Its based on the Gilbert Cell.

    http://www.techlib.com/electronics/amxmit.htm
     
    Last edited: May 26, 2009
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