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detector diode in so called crytal radios

Discussion in 'General Electronics' started by SimonLW, Feb 23, 2006.

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  1. SimonLW

    SimonLW Guest

    I remember building these as a kid. The reason for the diode makes sense,
    but wouldn't the signal have to be strong enough to break over the forward
    voltage drop of around .25 volts for the germanium diode? If so wouldn't a
    weaker AM signal get chopped off and distorted when the modulated signal is
    at the minimum point?

    Please help me clarify how this really work. I'm obviously missing
  2. Chris

    Chris Guest


    The radio signal from crystal palace is very strong. The germanium diode
    exploited to non linear charactistic curve of the diode to act as a square
    law detector. Probably as high as 1/2 a volt with an attena 20 foot long.
    Volts per meter x meters.... Might have been strong enough to light a bulb.
    In mum's family the six of them had an earphone each of a crystal radio.

  3. Chris

    Chris Guest


    Grandad sold a crystal set with a loudspeaker it had a "germanium triode"
    amplifier his step brother Walter invented. In fact it might have been my
    Uncle Arthur who invented this triode before the loony psychiatrists put a
    knife through his head....

    The world is mad - I now know the surgeon who worked out the "treatment" he
    lives almost next door and his name in Richard.
  4. SimonLW

    SimonLW Guest

    Perhaps I should connect the antenna and diode to my tin foil hat. I could
    tune in a station by adjusting my glasses.
  5. Wdino

    Wdino Guest

    The "crystal set" simply needs some form of voltage no-linearity to
    demodulate an AM signal. The voltage does not have to be above the knee
    voltage of a diode but just be operating in the non-linear part of the
    diode curve.

    When I was a kid I made a "crystal set" using a razor blade as the
    detector. Apparently this was a simple form of Schottky diode. It was
    very sensitive.
  6. MG

    MG Guest

    No need for the diode if you have filling in your teeth.

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