Low Power AM Transmitter

Posted: September 21, 2009 in Communications

This is a project during our 5th year in college, a low power AM transmitter, this transmitter can reach up to 150ft and can transmit at frequencies from 697 to 896 Khz. This transmitter consist of a clapp oscillator, a buffer, RF amplifier  and modulating signal driver. The oscillator can be tweaked to operate to other frequencies by tweaking C6 and the RED IF coil. If using other input device other than the EM80 microphone such as MP3 players, resistor R8 must be disconnected.  Another thing in building this transmitter is that the PCB layout is critical specially in the oscillator section because of the high frequencies involved.

Click image to view the full schematic

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Comments
  1. Zee says:

    Hi! We made an AM transmitter using your circuit diagram but unfortunately we couldn’t transmit longer than 1 foot away? What did you made to transmit it to a longer range?

  2. tiktakx says:

    put a 1hz testone and check if you are getting about 50V pk-pk at the your antenna, adjust the RED IF where the antenna if necessary, also I think I interchanged C4 and C5 at the oscillator side, please check if you are getting around 5V or above at the oscillator before it enters the buffer, and the PCB layout is also critical

    • Zee says:

      ok thanks. we’ll try it tomorrow. by the way, with the default circuit, is the antenna just a simple AWG #22 wire? is it necessary to connect it to the ground?

  3. Tien Nguyen says:

    (Sorry, I’m not good at English)
    Hi, I’m going to make AM transmitter using your circuit diagram but I don’t know how to make “RED IF” and antenna in pratice. And I want to learn to compute the value of devices in this circuit. Do you have any document about computing this circuit ? Can you share it?
    Thank for sharing !

  4. tiktakx says:

    the red if can be bought from any electronics store, it is usually used in radios they are sometimes called IF transformer. The documents are misplaced but you can derive the parts using baisc equations from amplifier design. Just an errata C4 and C5 values are interchanged 😀

  5. paul says:

    tiktakx, where will i connect the other RF amplifier so that it will become a stagger type and are the values of the first RF amplifier the same as the second one? thank you and godbless?

  6. nadir says:

    can u send me its ac and dc analysis i made it it works

  7. marlon says:

    pcb layout can you post it sir.. i need it for our project please

  8. shall i remove the capacitor in the RED IF COIL?

  9. red if coil- un nasa am radios po ba un?

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