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Two-way RF communication

Discussion in 'Radio and Wireless' started by Will777, Sep 2, 2010.

  1. Will777

    Will777

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    Sep 2, 2010
    Hi there,

    I am interested in building a RF-communication project - i.e. like walkie-talkies. I live in South Africa - there are loads of two-way radio's available for purchase but I would like to build this myself as a hobby project.

    In terms of range I am thinking of anything up to 1 km.

    Can anyone point me in the right direction - kits, schematics?

    Thanks
     
  2. rob_croxford

    rob_croxford

    262
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    Aug 3, 2010
  3. Will777

    Will777

    31
    0
    Sep 2, 2010
    Hi Rob,

    Thanks for your reply - the second link is broken - could you repost please?

    An update to my question - I found the following site http://www.gw1tdv.co.cc/ which features a circuit:

    [​IMG]

    This would be ideal for what I plan to do - the only thing I am unclear about is the component labelled "X1" - is this a crystal and how would I know what frequency?

    The text with the circuit states that the two units operate on 49.860MHz for one unit and 49.410MHz for the other. Is this the frequency of the crystal?
     
    Last edited: Sep 2, 2010
  4. rob_croxford

    rob_croxford

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    Aug 3, 2010
    Yes X1 is the crystal (i believe). and it will be rated at 49.860MHz. This crystal can be bought at that frequency so no step downs are needed. I beleive alot of walkie-talkie type projects/products use this frequency crystal.
     
  5. Will777

    Will777

    31
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    Sep 2, 2010
    Thanks for the info.

    Seeing as these units are meant to run in duplex more, am I correct in saying that the frequencies need to be different on the two units? So that means I get the one crystal in 49.860MHz and the other in 49.410MHz?

    Pardon my ignorance, I am learning new things about this hobby every day :)
     
  6. rob_croxford

    rob_croxford

    262
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    Aug 3, 2010
    I assume they should both opperate at the same frequency. Are you sure you do not want them to run at hald duplex? ( like most walkie talkies only one can "talk" while the other "listens" however the amount of people who listen is unlimited )
     
  7. Will777

    Will777

    31
    0
    Sep 2, 2010
    This is supposed to be a radio intercom that you can use on a motorcycle to communicate to your passenger. The site states: "As it is difficult to use a PTT on a motorbike a continuous transmission / reception duplex system was required."

    So I guess it has to run in full duplex?
     
  8. rob_croxford

    rob_croxford

    262
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    Aug 3, 2010
    Oh ok i understand. Yes well then i assume you will need two sepperate frequencies with each walkie talkie continuously tuned into the other. you will also not be able to use the same circuitry for the mic as you do for the speaker (simply reverse the current) as there will be no switching mechanism.
     
  9. Will777

    Will777

    31
    0
    Sep 2, 2010
    Not sure I understand - this diagram shows the mic on bottom left (close to the 330R resistor) and the loudspeaker on the right?
     
  10. rob_croxford

    rob_croxford

    262
    0
    Aug 3, 2010
    Yes but with many conventional walkie talkies (where only one person at a time talks and the other listen) The PTT is used to reverse the opperation of the loudspeaker. In basic terms this means that it opperates the other way, so rather than convert electrical energy into mechanical it converts mechanical energy into electrical and therfore doubles up as a mic. This generally saves costs and space.
     
  11. Will777

    Will777

    31
    0
    Sep 2, 2010
    Ok, that makes sense when the loudspeaker is also the mic - but with this design, where the mic and loudspeaker is separate would I still need to reverse the current?
     
  12. rob_croxford

    rob_croxford

    262
    0
    Aug 3, 2010
    no, sorry i thort you were making a conventional 2 way radio project. as you are using a seperate mic and loudspeaker the current will not need to be reversed

    cheers
     
  13. Will777

    Will777

    31
    0
    Sep 2, 2010
    Hey Rob, thanks for all your assistance, you've really helped me out a lot
     
  14. rob_croxford

    rob_croxford

    262
    0
    Aug 3, 2010
    No problem. good luck!
     
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