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GPRS PCMCIA card - antenna matching Q

Discussion in 'Electronic Design' started by Peter, Mar 17, 2005.

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  1. Peter

    Peter Guest

    Hi All,

    I am using a Sierra 750 GPRS card

    http://www.sierrawireless.com/ProductsOrdering/AC750_GSM.asp

    but I am connecting an external antenna to it via about 1ft of 50 ohm
    coax cable.

    The external antenna is in an ix104 tablet computer and if you like a
    lot of reading the details are here :)

    http://www.peter2000.co.uk/ix104/index.html

    I have no data on the ix104 external GPRS antenna characteristics but
    it is certainly a lot smaller than the little rod one that comes with
    the 750 card.

    To connect to the 750, I cut off the rod of the antenna which comes
    with it and solder the coax direct to the RF connector which forms the
    base of the antenna.

    Unfortunately there are several components (capacitors and inductors)
    on a tiny PCB at the base of the antenna. I can't avoid damaging these
    when removing the plastic moulding.

    The finished thing does work! The sensitivity appears comparable to
    e.g. a Nokia mobile phone, so I am content with it. However I am
    concerned about the VSWR resulting from an impedance mismatch - can it
    damage something?

    I know about hardware/software but my RF knowledge is minimal.


    Peter.
     
  2. James Meyer

    James Meyer Guest

    If it works, don't sweat the small stuff. There isn't enough power
    available in a typical cellphone output stage to damage anything even with 100%
    of its output reflected back.

    Jim
     
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