Problem in FM transmitter

Discussion in 'Wireless & RF Design' started by prsarr, Jul 9, 2012.

  1. prsarr

    Thread Starter New Member

    Jul 8, 2012
    I have made an FM transmitter on a breadboard using a single transistor, BC547... Sometimes I can hear the music on my cell phone at a frequency of 100.35 MHz but mostly its all noisy... What can I do to remove the noise??? I am using a battery of 9V. Will a voltage regulator help in reducing noise?? Also plz tel any precautions to be taken when i build the circuit on a simple circuit booard... Plz help... Thanx
  2. TecknoTone

    New Member

    May 20, 2012
    Breadboards are not suitable for RF circuits as there is too much stray capacitance.
  3. praondevou

    AAC Fanatic!

    Jul 9, 2011

    Yes, breadboard is not good and also: Where is the schematic and breadboard layout picture?
  4. vk6zgo

    Active Member

    Jul 21, 2012
    Noise free reception using FM relies on a number of things:-

    ( 1)Signal strength--Your BC547 will be really battling to produce much power at 100MHz,plus the FM receiver in your cell phone is not very sensitive.
    This means that you will lose noise immunity.

    (2) Sufficient frequency deviation-The FM Broadcast system standard is +- 75kHz max deviation.
    Anything much less than that causes the demodulated signal to be very low in amplitude,so that the lowest level passages of music will be eclipsed by circuit noise.
    You are unlikely to achieve a lot of deviation in such a simple circuit.

    (3) Frequency Instability---- Although the FM receiver is quite wideband,
    self-excited oscillators at 100MHz or so can easily drift out of the passband,& the receiver will need retuning.

    All these limitations mean your received audio will be very low level & noisy,& make it unlikely that the thing will ever be anything but an interesting experiment.
  5. DickCappels


    Aug 21, 2008
    Yes, by all means, post the circuit. Also, please describe the noise you are hearing and the audio signal you are feeding into the transmitter (over driving the transmitter can make the signal sound noisy on the FM receiver). Oh yeah...and get rid of the breadboard.
  6. radiohead

    Active Member

    May 28, 2009
    It is possible make a static-free simple one-transistor transmitter on a breadboard with no problem. Can you post a schematic of the circuit you're using and a photo of your breadboarded circuit?

    Also, use a wide band receiver for best results.