Walkie Talkie - mic/speaker crossing

Discussion in 'The Projects Forum' started by smsdalle, Dec 12, 2013.

  1. smsdalle

    Thread Starter New Member

    Dec 9, 2013
    4
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    HI circuit-people.. I'm new here, but still need help :)

    I'm working om making my own "simplex/duplex repeater" for walkie talkies..

    What I'm doing/have done, is that I have soldered two walkie talkies together, by crossing speaker and mic from the two.

    The idea is, that one walkie receives a signal (voice) and when that sound is supposed to come out the speaker, it goes directly into the others mic (a clean signal) and vise versa..
    Both walkies have Vox activated, so that they start transmitting when receiving sound in the mic..
    They're on different channels, so I can send receive over larger distances.

    So I've done it, but run into a problem, and here I need your help.. I can push the call button on a walkie and the sound goes clean through... But if I start talking, then my voice only comes through a little but with a whole lot of noise and cratching and I can barely hear my own voice..

    So my question; Do I need some kind of resistor or anything between the speaker and mic?
     
    Last edited: Dec 12, 2013
  2. smsdalle

    Thread Starter New Member

    Dec 9, 2013
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  3. smsdalle

    Thread Starter New Member

    Dec 9, 2013
    4
    0
    and this is the mic, when it's not on the board

    [​IMG]
     
  4. smsdalle

    Thread Starter New Member

    Dec 9, 2013
    4
    0
    artist rendering of what I'm doing.. for dummy's (myself)

    [​IMG]
     
  5. MrChips

    Moderator

    Oct 2, 2009
    12,425
    3,359
    Microphones and speakers have different impedances and circuit requirements.
    You cannot use the speaker output circuit to replace a microphone.
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    This will not work if the receive frequency on Walkie A is close, or the same, as the transmit frequency on Walkie B. You must use "duplex" frequency diversity when making a repeater, the greater the frequency separation, the better. Commercial repeaters use a frequency separation of 5 MHz at 450MHz, and even then they must use huge cavities (RF duplexor) to keep the repeater's transmitter from desensitizing the repeater's receiver.

    The only way of making a "simplex" repeater is to make it a store-and-forward message system. You would have digitize the voice message, wait for dead air, and then retransmit the voice message on the same frequency.

    The distortion of the signal is likely caused when the transmitter overloads the repeater receiver...
     
    Last edited: Dec 12, 2013
  7. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,972
    744
    The signal from the speaker is too loud, you need to attenuate it with a volume control.
     
  8. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    1,438
    368
    As well as attenuation you should also couple the audio with a small capacitor in each wire and keep the radios as far apart as possible.
     
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