Help in making FM transmitter

Discussion in 'Wireless & RF Design' started by Chaitanya_om, Sep 11, 2010.

  1. Chaitanya_om

    Thread Starter New Member

    Sep 11, 2010
    Hello everyone, I m making FM transmitter.Circuit diagram is shown in attachment.
    I m building it on bread board.One time it work perfectly after it is not working i also check transistors.I add var cap in parallel with inductor for tuning,i can also receive it on my receiver but i herd pulses may be from oscillator.
    When i disconnect amplifier (T1) from T2 i get perfect frequency but after applying AF to base it is't work plz help.
  2. Wendy


    Mar 24, 2008
    How long have you had it? It does sound like something died or went out. I'd be suspicious of the electrolytic caps. If they shorted they would connect the stages. Measured any voltages?
  3. skeptic

    Active Member

    Mar 7, 2010
    It would help a lot if you could post voltages at each node or junction.
  4. Audioguru

    New Member

    Dec 20, 2007
    A circuit built on a breadboard might work up to 1MHz. This project works at 100MHz which is much too high for the very high stray inductance and stray capacitance of a breadboard. Simply moving one of its many long wires would change its frequency a lot.
    Use a compact pcb or stripboard with all tracks cut short.
  5. Wendy


    Mar 24, 2008
    The OP did mention it used to work. The assumption is it was the same circuit, which suggests component failure.

    On the other hand, I did use the word assumption.

    I like the Manhattan_Construction_for_RF and the Dead Bug Prototyping myself.
    Last edited: Sep 24, 2010
  6. PRS

    Well-Known Member

    Aug 24, 2008
    Audioguru is right. Don't use a breadboard. Build your circuit on a copper-clad board using short paths for high frequency signals.