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Discussion in 'General Electronics Discussion' started by gramoca, Nov 22, 2011.

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  1. gramoca


    Nov 22, 2011
    Is it possible and/or difficult to have a receiver and a small cigarette-sized transmitter that, when the transmitter is at a certain distance from the receiver, and the signal is broken, the receiver will emit and audible signal? Would this also work with multiple that the receiver would issue the same audible signal when any one of the transmitters were out of range?

    Thanks for helping....
  2. davenn

    davenn Moderator

    Sep 5, 2009
    Hi Gramoca
    welcome to theforums :)

    unfortunately its very difficult to do something like that as radio waves dont just go a certain distance and then stop.
    Their propagation and distance/area covered depends on many factors like....
    frequency, power level output, objects in the path that can absorb and or reflect the radio signals. It also depends on the sensitivity of the receiver

    it isnt possible to make a radio signal travel say... only 5 metres ( or 10 or 50 or 1km etc) then stop.

  3. gramoca


    Nov 22, 2011
    Thank you for the response....This makes perfect sense....
  4. BobK


    Jan 5, 2010
    It can think of a way to do it, but it would not be cheap. Each transmitter and the reciever would need a GPS. The transmitters would contnually transmit their positions and the receiver would calculate the distance from it's position, and sound the alarm when any transmitter was out of range.

  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    The other way is to do it like radar (or sonar).

    Each box (or the ones that have to raise an alarm) send out a coded pulse. The other end, when it receives the pulse (probably one that is coded for it) responds with an echo. This is received and the elapsed time is used to estimate distance.

    For relatively short distances (consider the speed of sound cf the speed of light) it is easier to do this with an ultrasonic chirp.
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