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Aligning Keychain Remotes

Discussion in 'Electronic Repair' started by [email protected], Mar 3, 2005.

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  1. Guest


    I own a 52-unit apartment complex. About a year and a half ago, I
    installed power gates. The power gates use a Multicode 300MHz
    receiver, and I issue keychain remotes to all the tenants. I am having
    a problem with the remotes dying. At thirteen bucks a remote, it
    adds up fast.

    These are very simple units, and I suspect they're mostly just
    going out of alignment. Without going to the trouble of tracing the
    circuit, they have:

    * A one-transistor RF oscillator
    * A ten-place DIP switch
    * A single DIP IC - presumably a shift register to serialize the
    DIP switches
    * A variable capacitor - one would suppose, to tweek the freq.
    * A potentiometer - to adjust the low frequency pulse oscillator?

    When you press the switch, the remote emits a single squirt of
    pulsed 300MHz RF.

    The problem is: how to measure it? You can't just stick a counter
    on it, because it's pulsed. I'm thinking to use an RF oscillator and
    a mixer going to an audio amp - when the oscillator is close enough to
    the remote, I'll hear it heterodyne. I don't think it needs to be
    super accurate. Or maybe a scope with an XY input for lissajous

    - Jerry Kaidor ( )
  2. Rono

    Rono Guest

    For 600 mhz approx. units, I used a Yaesu FRG-4900
    Communications receiver! Rono.
  3. Guest

    Unfortunately, I don't have a receiver that covers 300MHz.
    Essentially, that's what my oscillator+mixer+amp setup would be -
    an ad-hoc receiver.

    I just had a couple new ideas: Wonder where my old grid dip
    meter got off to? Think it's in the garage. Would it be accurate
    enough? Probably not....

    Might be the excuse I've been looking for to buy an old HP
    spectrum analyzer :).

    I just traced the thing's circuit. I think I've identified a node
    can be grounded to the battery to make the thing emit continuous
    wave RF. Then just belly it up to the frequency counter....
  4. NSM

    NSM Guest

    Use a receiver connected to a scope? How much is an extra gate receiver?
    I've seen items like this offered in "Ciarcia's Circuit Cellar".

  5. Guest

    The receivers cost $45 plus shipping. Not excessive. Might be a way
    to go. A spare receiver
    would be a sure go/nogo test for the alignment too.

    - Jerry Kaidor
  6. NSM

    NSM Guest

    And a useful backup!

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