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Simple Short Range FM Transmitter

Discussion in 'General Electronics Discussion' started by Einstein Jr., Oct 22, 2014.

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  1. Einstein Jr.

    Einstein Jr.

    21
    0
    Oct 21, 2014
    Hi, I am trying to make a short range(around 50 - 100 meters) fm transmitter and found this simple one on the web(simplest transmitter.png). I want it to have different input options 1. the jack, 2. regular microphone, and then I wanted to have a sonic ear type amplified mic for the third option. I thought If I put a switch which had three inputs I could do that. However for the mic I would need an extra transistor to ampliphy it a little right? How would I do that? Also, I would like to attach an anttena but I don't understand how I would attach it because there is a ground connection with it. I have never heard of an anttena with polarity? "My version" is sort of my idea of how I think i could be but I need help.
     

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  2. Fish4Fun

    Fish4Fun So long, and Thanks for all the Fish!

    451
    103
    Aug 27, 2013
    Hey Einstein Jr. !

    I think you might need to "re-think" simple....RF is really not my forte, but what little I have played with it, I have never found a "simple" answer to reliable DIY FM Rx/Tx starting from the component level....PCB layout, grounding and passive component matching play such a critical role that w/o a fairly extensive background failure is eminent....and it would APPEAR to me that this "simplest_transmitter" circuit is Amplitude Modulated, not Frequency Modulated (AM, not FM...), but I could certainly be mistaken......

    Depending on what you actually want to achieve, you might consider re-purposing a set of FM walkie-talkies...likely available for < $10 at a store near you....and very likely to "work out of the box".....Or, you might consider something like: http://www.ebay.com/itm/1pcs-DC-5V-...335?pt=LH_DefaultDomain_0&hash=item4187da890f .....BUT, Please understand the latter module is designed to be controlled by a uController and will likely be difficult for you to do anything with w/o some pretty good coding skills....

    Good Luck!

    Fish
     
  3. BobK

    BobK

    7,673
    1,684
    Jan 5, 2010
    Actually it is not that difficult. A while ago I made a ~100MHz oscillator from a 2n2222 transistor and a coil of 4 turns of wire round around a pencil and a few capacitors and resistors. Feeding a microphone through a cap to base made an FM transmitter that I could broadcast to a nearby radio. All done on a solderless breadboard. Tuning was accomplished by changing the separation of the coils in the inductor. I doubt that I could reproduce the circuit though... I have no idea why the mic introduced frequency modulation, but somehow it did.

    Bob
     
  4. Einstein Jr.

    Einstein Jr.

    21
    0
    Oct 21, 2014
    I have solved most of my questions but can does anyone know how to do connect an antenna to that circuit. It seems like it has polarity and thats what is getting me confused. Also, I was wondering how you could wire in a mic, because the circuit was originally intended for mp3 player. Any suggestions appreciated!:)
     
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