Modifying old dish network dish for wifi

Discussion in 'Wireless Internet' started by gregbr549, Jun 18, 2007.

  1. gregbr549

    gregbr549 Guest

    Hi,
    I am new here. I am trying to modify an old dish network dish to get
    better wifi reception. I gutted the reciever part of the dish, hogged
    it out and made room for my USB Wireless Dongle. Will this work? Will
    it be any better than a tin can? Do I need to paint or cover the dish
    with aluminum foil? Here are some pics,
    Thanks
    Greg


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    gregbr549, Jun 18, 2007
    #1
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  2. Nice idea, but I don't think it will work very well.
    Where to start....

    No need for aluminium foil cover. There's plenty of wire mesh under
    the fiberglass. Or, if it's a metal dish, it will reflect 2.4GHz as
    well as the original 12-13GHz.

    The big problem is that you don't have a feed that is matched to the
    dish. In transmit, the USB dongle radiates in all directions. Most
    of it will get reflected to who knows where by the metal horn. My
    guess is about 1/10th of the radiated RF actually hits the dish and
    goes in the desired direction. In receive, it's not so bad. The USB
    dongle probably gets all the RF that is reflected from the dish.
    However, that means you'll have more gain in receive than in transmit.

    To see how this works, scan through this article on feed design.
    <http://www.w1ghz.org/antbook/contents.htm>
    <http://www.w1ghz.org/antbook/conf/high_efficiency_prime_feeds.pdf>

    The next problem is lack of gain. The maximum gain of a dish antenna
    can be calculated. Assuming you did everything perfectly, and the
    feed was properly matched to the dish f/D ratio, then:
    Maximum gain for a 0.6meter diameter dish:
    gain = 9.87 * Dia^2 / wavelength^2 * (feed efficiency)
    gain = 9.87 * 600mm^2 / 125mm^2 * 0.4
    gain = 91
    dBi = 10 log(91) = 19.5dBi
    The 40% efficiency (that's the 0.4) is probably optimistic.
    Again, that's if everything is lossless, perfectly matched, built
    correctly, and properly designed. I don't think your feed qualifies.

    Let's say that the USB dongle works as I described, where only 10% of
    the RF gets to the dish in transmit. 1/10th is:
    10 * log(0.1) = -10dB loss
    So your final gain will be about:
    19.5dBi -10dB = 9.5dB gain.
    That's not much more than a much smaller and easier to build biquad or
    coffee can antenna. That's also why you want to spend some time
    designing a proper matched feed.

    I don't really agree with these, but they might be of interest.
    <http://www.findmorecollectibles.com/wifi.html>
    <http://www.weijand.nl/wifi/>
    <http://www.qsl.net/ki7cx/wgfeed.htm>
    <http://www.engadget.com/2005/11/15/how-to-build-a-wifi-biquad-dish-antenna/>
    <http://www.nodomainname.co.uk/parabolic/parabolic.htm>
     
    Jeff Liebermann, Jun 18, 2007
    #2
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