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Using wire hanger as replacement wireless antenna = burnout?

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  • 27-08-2009 9:21am
    #1
    PaddyTheNth
    Registered Users Posts: 605 ✭✭✭


    I recently had reason to dig out a wireless card I put in my old pc a couple of years ago which had an external antenna which screwed in to the wireless card at the expansion slot.

    Having put the card into a new pc I couldn't find the antenna, and the card alone was pretty useless at anything more than a few feet from the router.

    So I had a mcgyver moment and untwisted a wire coat hanger, touched one end to the antenna connection and found I had very good signal strength.

    This worked fine for a couple of days - although I did get a bit of interference in my speakers until I moved a few wires which I guessed was coming from the unshielded antenna - but yesterday evening the signal strength was much weaker when I turned on the computer, and eventually it dropped to the point that I couldn't connect to the network at all. I've checked that the hanger is still in contact with the antenna and that its still in the same position/orientation and nothing has changed.

    None of the other computers on the network experienced any changes.

    So my question is, is it possible that my jury-rigged setup was causing the radio to transmit at full power the entire time (pure guesswork on my part, I don't know how it works) and I've managed to burn it out?


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    #2
    Fuzzy Clam
    Closed Accounts Posts: 3,293 ✭✭✭Fuzzy Clam


    :eek::eek::eek::eek::eek:

    At the very least there would have been an impedance mismatch.

    Chances are that your improvised aerial shorted out the connection.


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    #3
    PaddyTheNth
    Registered Users Posts: 605 ✭✭✭PaddyTheNth


    Fuzzy Clam wrote: »
    :eek::eek::eek::eek::eek:

    At the very least there would have been an impedance mismatch.

    Chances are that your improvised aerial shorted out the connection.
    I won't pretend to understand impedance mismatch, my electrical engineering knowledge is pretty much nonexistant.

    It worked so well for a while :(


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    #4
    Fuzzy Clam
    Closed Accounts Posts: 3,293 ✭✭✭Fuzzy Clam


    In short, the card is designed to "see" a particular load to operate properly. In the same way that your stereo is designed to work with 4 or 8 ohm speakers, in this case its 50 ohms.
    The correct aerial has an impedance (a sort of resistance) of 50 ohms. A random length of wire will be anything but 50 ohms (unless your very lucky).
    I guess it just put a bit too much stress on the output of the card.


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    #5
    PaddyTheNth
    Registered Users Posts: 605 ✭✭✭PaddyTheNth


    Makes sense.

    I guess I got the idea from when my radio antenna broke off when I was about 9 and I did the same trick. Should have realised that it makes a difference when you're transmitting as well as receiving!


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    #6
    watty
    Registered Users Posts: 32,417 ✭✭✭✭watty


    More likely static damage. Or some other issue. The real WiFi aerials are insulated.

    The power available isn't normally enough to cause PA damage due to mismatch. The "real" aerial length inside the plastic case is only a couple of centimetres.


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    #7
    Fuzzy Clam
    Closed Accounts Posts: 3,293 ✭✭✭Fuzzy Clam


    watty wrote: »
    The "real" aerial length inside the plastic case is only a couple of centimetres.
    Closer to about 7 cm.

    More like the op shorted the center by jamming in a coathanger. Never the less, it is possible to blow these by gross mismatch over time.


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    #8
    PaddyTheNth
    Registered Users Posts: 605 ✭✭✭PaddyTheNth


    FWIW the photo here is the sort of thing I was using.

    I didn't exactly jam anything in, just taped the hanger so it was touching the antenna. Got a replacement today anyway so back in business. I just found the gradual degradation in performace curious, as I would have thought it would have been either a working or completely broken situation.


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    #9
    watty
    Registered Users Posts: 32,417 ✭✭✭✭watty


    Fuzzy Clam wrote: »
    Closer to about 7 cm.

    More like the op shorted the center by jamming in a coathanger. Never the less, it is possible to blow these by gross mismatch over time.

    Depends if you measure the whole end fed dipole for 2.4GHz or just the end whip :) Or the whole external plastic case.

    Only units capable of illegal power level or badly designed can be damaged by mis-match. I design this sort of stuff for a living, which is how I know.


    Glad to hear you are sorted. :)


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    #10
    Fuzzy Clam
    Closed Accounts Posts: 3,293 ✭✭✭Fuzzy Clam


    watty wrote: »
    depends if you measure the whole end fed dipole for 2.4GHz or just the end whip :)

    With you now.


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    #11
    Fuzzy Clam
    Closed Accounts Posts: 3,293 ✭✭✭Fuzzy Clam


    PaddyTheNth wrote: »
    FWIW the photo here is the sort of thing I was using.

    I didn't exactly jam anything in, just taped the hanger so it was touching the antenna. Got a replacement today anyway so back in business. I just found the gradual degradation in performace curious, as I would have thought it would have been either a working or completely broken situation.

    I have one of those Canyon cards here. Found it quite good.

    Its possible, and I'm only guessing, that the "final amplifier" stage of the card was damaged. The weaker signal may have come from an earlier part of the circuit. I could be completely wrong, of course.


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