FM Transmitter project

Discussion in 'The Projects Forum' started by iceradaph, Oct 29, 2013.

  1. iceradaph

    Thread Starter New Member

    Oct 29, 2013
    2
    0
    Greetings, I'm working on a FM Transmitter project. I've tried building other FM circuits but sadly, I got none of them to work. I don't know if I did something wrong or the circuits that I built were simply bad designs, so i want to ask everyone if this circuit would work. Thanks :)



    [​IMG]
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    How did you try to build those transmitters?
    They can not be made on a breadboard as the stray capacities will destroy all RF signals.
    A better way is using perf board or even better would be biuilding it using the manhatten style.
    (see the attached PDF's).

    Bertus
     
  3. iceradaph

    Thread Starter New Member

    Oct 29, 2013
    2
    0
    I made them using a PCB, none of them worked though. When I check the output, I couldn't even get a carrier frequency
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    Can you post a picture of the top and bottom of your FM transmitter?
    That way we can see if there are construction failures.

    Bertus
     
  5. radiohead

    Active Member

    May 28, 2009
    474
    31
    It's not that the transmitter doesn't work, it's probably transmitting outside the frequency range of your receiver. If you have a standard broadcast band radio and are trying to tune in to that band, you may have to adjust the trimmer cap and/or experiment with the coil it is in parallel with. Use a solid-core wire for the coil. Make several coils: one with 5 turns, one with 6 turns, one with 7 turns, and one with 8 turns (use a phillips screwdriver as a former and keep the turns tight together). Remember the fewer number of turns, the higher the frequency will be. Likewise, the more turns, the lower your frequency will be. If you can't receive the signal, replace the coil and adjust your trimmer until you have feedback on your radio. If there is no signal, replace the coil and adjust the trimmer again. Keep doing this until you finally find the signal.
     
  6. Papabravo

    Expert

    Feb 24, 2006
    10,138
    1,787
    What makes you think that an FM radio can detect the presence of a carrier signal. It detects changes in frequency. That's why yelling louder into the microphone of an FM transmitter has absolutely no impact on the sound coming out of a receiver.
     
  7. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
  8. vk6zgo

    Active Member

    Jul 21, 2012
    677
    85
    Can you run that past me again?:D
     
  9. Art

    Distinguished Member

    Sep 10, 2007
    785
    61
    Looks awesome, but why do that when there are protoboards full of dots?
     
  10. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    With the manhatten style prototyping, you will have a ground plane and more freedom of placing the parts.

    Bertus
     
  11. Papabravo

    Expert

    Feb 24, 2006
    10,138
    1,787
    Sure an FM transmitter converts amplitude into frequency deviation. Yelling into a microphone will increase the deviation up to a point. Once the maximum deviation is reached you get any more.
     
  12. vk6zgo

    Active Member

    Jul 21, 2012
    677
    85
    With respect,thats not what you said!

    This is what you posted:

    "What makes you think that an FM radio can detect the presence of a carrier signal. It detects changes in frequency. That's why yelling louder into the microphone of an FM transmitter has absolutely no impact on the sound coming out of a receiver."

    Listening to an FM Broadcast of a Symphony Orchestra,you may hear everything trom the audience coughing before the music starts,to the extremely high sound level of the full Orchestra.

    Actually,you don't hear the full concert Dynamic Range as there are limiters to prevent the Transmitter exceeding its permitted deviation.
    The Dynamic Range is nonetheless,pretty good,& can easily handle "from a whisper to a shout".

    In a Communications Transmitter,intelligibility is of greater importance than Dynamic Range,so the audio is limited more savagely.

    In both cases,the limitation of deviation is not inherent in the type of modulation,but is imposed to meet other requirements.

    And,yes,an FM receiver will detect the presence of an unmodulated carrier signal.
    In the absence of any signal,an (unmuted) FM receiver will produce a constant "hiss".
    As it tunes over the carrier,the hiss level will reduce sharply,an effect known as "quieting".
     
Loading...