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Some More Simple FM Transmitters

Discussion in 'Electronic Projects' started by Iceman_Chris, Nov 28, 2004.

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  1. leejongfan

    leejongfan New Member

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    Hi all,

    I am going to construct the FM transmitter according to following schematics using veroboard : Miniature FM Transmitter #4 from Atoon website (the right most pictures in the 1 post of this thread)

    As far as I know, components layout is very critical in RF circuit. Anyone has experience in this, please help.

    Your support would be much appreciated. Thanks!
     
  2. audioguru

    audioguru Well-Known Member Most Helpful Member

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    It is not a good FM transmitter:
    1) Its antenna is connected to its oscillator so its frequency will change if something gets near the antenna or moves away.
    2) It doesn't have a voltage regulator so its frequency will also change as the battery runs down.
    3) It doesn't have pre-emphasis (treble boost) like all FM radio stations so the de-emphasis in all FM radios will cut the highs and sound like a stereo with its treble tone control turned all the way down, or like an AM radio.
    4) It is mono, not stereo like a Micromitter.

    I made the very simple circuit about 45 years ago. Its performance was poor.
     
  3. leejongfan

    leejongfan New Member

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    How about the Miniature FM transmitter #1 (Atoon website)
    Let's say actually I don't really concern about sound quality as well as power supply, then are there anything else I should pay attention to?
    For the antenna problem, do you mean I should place the atenna far way from the trimmer capacitor?
    Thanks!
     
  4. dave

    Dave New Member

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  5. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The antenna of the very simple FM transmitter is connected directly to the oscillators tuned circuit. Anything that gets near the antenna or moves away changes the capacitance at the antenna and at the oscillator's tuned circuit which changes the oscillator's frequency.
    My FM transmitter has an RF amplifier between the oscillator and the antenna so its frequency does not change.

    It doesn;t have a voltage regulator like my circuit so you must retune it as the battery runs down.
     
  6. chilinski

    chilinski New Member

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    I'd like to see the backside of this. Would you post a photo of it?
     
  7. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I made my FM transmitter 3.5 years ago.
    The stripboard is just 12 horizontal parallel strips of copper. Some of the strips were cut with a drill bit and so the strip was used for two or three functions. Eadh part has its own holes. A few vertical jumper wires are on the parts side of the stripboard. Most of the parts are also vertical.
     
  8. vinate

    vinate New Member

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  9. prabrahim

    prabrahim New Member

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    Sir,
    Thanks for ur circuit,
    does it work well
    does it need an antenna
     
  10. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I was not knighted by the Queen of England so I am not a SIR.

    My Mod-4 FM transmitter sounds excellent, its frequency does not change when something move near or moves away from its antenna nor when the battery voltage runs down and its range is more than 2km to a very sensitive FM receiver when its 9V alkaline battery is new and there is nothing in between.

    Of course it needs an antenna. It is a radio transmitter.
    I never tried it without an antenna.
    Without an antenna then its range might be across the street if it is in a plastic box.
    I tried it without a battery but it didn't work.
     
  11. mvs sarma

    mvs sarma Well-Known Member

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    Nice reply Audioguru.
     
  12. Ammarjaasj

    Ammarjaasj New Member

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    thans alot
     
  13. transistor495

    transistor495 Member Forum Supporter

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    Adding a 2N3866 stage will boost the power about 4times. A matching dipole antenna can provide a range upto 4km.
     
  14. mvs sarma

    mvs sarma Well-Known Member

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    Thereafter you will stop all the woks and attend police staions to attend court cases for illegal broadcasts/transmissions.
     
  15. transistor495

    transistor495 Member Forum Supporter

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    I know it msv sarma. I have done it and tested it but now I'm using it without any antenna of course not even a short wire! I can receive signal within 200 metres circle without assistance of any cop.
     
  16. audioguru

    audioguru Well-Known Member Most Helpful Member

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    A serious problem with an illegal radio transmitter is the harmonics that cause interference to radio communications (ambulance or police radios?) and TVs.
     
  17. transistor495

    transistor495 Member Forum Supporter

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    Previously when I was in college hostel, I have assembled one fm transmitter. My hostel room was near to TV hall. I was able to interrupt the TV signal completely with my transmitter when trimming to some particular frequency. So when my friends are enjoying TV programmes I could annoy them with my transmitter kept in my pocket making ON/OFF. When it is interrupted some person( TV operator guys :D ) will try to fix it on tuner. No result!
    What I will do? I will go there and just touch on the TV same time I will switch off the transmitter. Wow!! I could here 'Well done,claps' from surroundings :D :D
     
  18. kandiraja

    kandiraja New Member

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    i want to build a remote controlled(radio frequency) race car for my project i am a beginner so iwant entire list of components and cicuit to connect them help me please....................
     
  19. mvs sarma

    mvs sarma Well-Known Member

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    welcome !
    why not purchase one?
     
  20. vanraj1

    vanraj1 New Member

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    Thanks i found some of very uewful porject to transmit FM if any one have FM reciver booster circuits diagram
     
  21. mvs sarma

    mvs sarma Well-Known Member

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    WELCOME !
    How far is FM Transmitter from your location. Because, it is Line of sight and difficult to use amplifier, unless you get a signal by skip zone effect. You can get many of them if you google, but the antenna has be installed like multi element Yagi cut to frequency you are likely to get.
     
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