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Hacking a "wireless" intercom

Discussion in 'Electronic Design' started by Norm Dresner, Apr 30, 2004.

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  1. Norm Dresner

    Norm Dresner Guest

    The "wireless" intercom I bought (2 stations) isn't wireless at all but uses
    the house wiring as a transmission medium. This means that it's use is
    restricted to one phase of the 2-phase 240v AC service in the house. I
    tried the simple expedient of jumpering the two phases with a HV 560 pf
    capacitor but got no transmission across to the second phase. I will
    probably run an extension cord between floors to allow me to at least
    temporarily use the devices but I'd really like to fiud some way to make it
    work anywhere in the house. To do that, I believe that I need to find out
    what kind of signal the device really couples to the AC main [the "manual"
    simply says that it uses FM which isn't very informative]. What's a
    reasonably simple circuit I could construct to tap into the AC where it's
    plugged in to allow me to see a high-frequeny
     
  2. Norm Dresner

    Norm Dresner Guest

    The "wireless" intercom I bought (2 stations) isn't wireless at all but uses
    the house wiring as a transmission medium. This means that it's use is
    restricted to one phase of the 2-phase 240v AC service in the house. I
    tried the simple expedient of jumpering the two phases with a HV 560 pf
    capacitor but got no transmission across to the second phase. I will
    probably run an extension cord between floors to allow me to at least
    temporarily use the devices but I'd really like to fiud some way to make it
    work anywhere in the house. To do that, I believe that I need to find out
    what kind of signal the device really couples to the AC main [the "manual"
    simply says that it uses FM which isn't very informative].

    1. What's a reasonably simple circuit I could construct to tap into the AC
    where it's
    plugged in to allow me to see a high-frequeny signal riding on top of it?

    2. What other methods might I use to determine what kind of signal they're
    creating?

    Thanks
    Norm
     
  3. Dave VanHorn

    Dave VanHorn Guest

    I will
    I hope you don't plan to cross-connect the phases.. That will be a brilliant
    idea, until the lights go out, and the smoke starts..

    The carrier is usually 20-50 kHz There's no easy and safe way to do what
    you're looking to do.
     
  4. Ken Taylor

    Ken Taylor Guest

    Agreed, big time. Take back the unit and get a true wireless one if this
    suits your purposes better. Stuffing about with the existing one will
    compromise its electrical safety.

    Ken
     
  5. Spajky

    Spajky Guest

    those intercoms (I inspected one way ago)
    use FM on LV (100 - 300 kHz; 3ch band, so 3 pairs can use one phase)
     
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