Parabolic dish with usb wireless

Archived from groups: alt.internet.wireless (More info?)

hi,

>From what i've read about usb wireless on
http://www.usbwifi.orcon.net.nz/, it looks like you stick a usb
wireless stick in the focal point of a reflective parabolic dish. Is
that with no fiddling with the usb adapters built in antenna? Because
this might be the road that i go down rather than searching for
pigtails for various different cards and being ripped off.
Thanks in advance.
5 answers Last reply
More about parabolic dish wireless
  1. Archived from groups: alt.internet.wireless (More info?)

    On 12 Dec 2004 14:34:33 -0800, sc.young@gmail.com wrote:

    >>From what i've read about usb wireless on
    >http://www.usbwifi.orcon.net.nz/, it looks like you stick a usb
    >wireless stick in the focal point of a reflective parabolic dish. Is
    >that with no fiddling with the usb adapters built in antenna? Because
    >this might be the road that i go down rather than searching for
    >pigtails for various different cards and being ripped off.

    Fiddling is done with a fiddle or violin. What manner of butchery
    were you trying to avoid? As for getting ripped off, wanna try to
    build your own from parts? You won't like the connector prices.

    The basic problem with shoving a USB dongle at the focus of a dish or
    corner reflector is illumination efficiency. Maybe an optical analogy
    is easier to understand. The USB dongle does a fair job of radiating
    equally in all directions, very much like a light bulb. I you put a
    reflector behind the light bulb, you'll have some of the light emitted
    by the light bulb reflected from the reflector, but the greatest
    majority of the bulbs light will end up going in directions where you
    don't want it to go. This is called "overspray". The same thing
    happens to 2.4Ghz wireless. Much of the signal is lost and not
    reflected. Oh yeah, just to make life interesting, the best
    efficiency a mesh or solid reflector can do is about 50% (losing -3dB
    gain). Obviously, a reflector will improve the gain of the insipid
    tiny PIFA antennas used in most USB dongles. Anything is an
    improvement. However, don't expect spectacular gain and you will see
    LOTS of side lobes.

    See:
    http://www.w1ghz.cx/antbook/chap4.pdf
    for a great tutorial on dish design that includes quite a bit on
    illumination issues.

    Personally, methinks the way to go with USB is removing the PIFA
    antenna and replacing it with an SMA connector. The connector would
    then go to a proper panel, patch, biquad, or dish antenna. At least
    all the RF goes to where it's suppose to end up.


    --
    Jeff Liebermann jeffl@comix.santa-cruz.ca.us
    150 Felker St #D http://www.LearnByDestroying.com
    Santa Cruz CA 95060 AE6KS 831-336-2558
  2. Archived from groups: alt.internet.wireless (More info?)

    >The basic problem with shoving a USB >dongle at the focus of a dish or
    >corner reflector is illumination efficiency. >Maybe an optical analogy
    >is easier to understand. The USB dongle >does a fair job of radiating
    >equally in all directions, very much like a light >bulb. I you put a
    >reflector behind the light bulb, you'll have >some of the light
    emitted

    So you mean that it is okay for focusing the signals that its receiving
    BUT the improvement in transmission is not that much. And what's the
    point of receiving a wireless signal if you can't send back a reply
    from a distance (unless you just want to use it to capture packets).
    Therefore you need a parabolic dish at both ends to pick up each others
    weak and misdirected signals. Am i right in interpretation of what you
    said?

    My initial thoughts was that it would be not much better at sending a
    signal but i thought that i was wrong. Based on my knowledge of
    constructing solar concentrators/furnaces.

    How is it good for wardriving? (Not that this is what i want it for but
    another guy mentioned this) You would only be seeing an increase in
    reception ability and not transmission strenght therefore what's the
    point if you can see all these networks but can't talk to them any
    better.

    Slowly i'm piecing together the general workings of the field at
    practical level.

    BTW, i can get one rp-sma + one n type connector for around $6-7.00
    which is what you need for a lot of cards (eg. netgear) therefore
    building a pigtail isn't that expensive BUT you probably need a crimper
    for the rp-sma.. or do you?

    Thanks,
    Stephen
  3. Archived from groups: alt.internet.wireless (More info?)

    On 12 Dec 2004 14:34:33 -0800, sc.young@gmail.com wrote:

    >hi,
    >
    >From what i've read about usb wireless on
    >http://www.usbwifi.orcon.net.nz/, it looks like you stick a usb
    >wireless stick in the focal point of a reflective parabolic dish. Is
    >that with no fiddling with the usb adapters built in antenna? Because
    >this might be the road that i go down rather than searching for
    >pigtails for various different cards and being ripped off.
    >Thanks in advance.

    I made a parabolic reflector for war driving using the below pdf
    template, and use it with a Microsoft USB wireless adapter that
    has a flip up antenna. Works pretty good and has noticable gain
    using the netstumbler signal strength display. Noticable
    improvement connecting to distant spots. Made it with a piece of
    thin cardboard to hold the parabolic shape, a piece of manilla
    folder with aluminum foil attached for the reflector, hot glue,
    and a hole in the cardboard to slip over the antenna at the
    appropriate point. It all depends on what your needs are
    (business vs. hobby) and how much $$$ you want to spend.

    http://www.freeantennas.com
    http://www.freeantennas.com/prod01.htm
    http://www.freeantennas.com/parabolic.pdf
  4. Archived from groups: alt.internet.wireless (More info?)

    sc.young@gmail.com wrote:
    > So you mean that it is okay for focusing the signals that its receiving
    > BUT the improvement in transmission is not that much. And what's the

    The reflector works in both transmit and receive.

    There will be noise received from the "back" side of the USB dongle as well
    as from the reflector side. Some other radiator would make more effective
    use of the reflector. That's not to say that the reflector doesn't help.
    The New Zealand site has some annectdotal data that says that a reflector
    improves the connection. I don't find the USB dongle to be very omni. I
    think it is heavily loaded toward the label side of the DLink-DWL-122.
    That would make the reflector more helpful than if it were a good omni.

    To your other question, Netstumbler only shows receive signal and noise.
    Some client programs provided with WiFi clients show "this signal" and
    "partner signal". That would be a better evaluator of the dish.


    I haven't used a reflector, but I have used a coffee can for a USB dongle.

    http://www.rahul.net/dold/clarence/usb-can/im000742-800x600.jpg
    http://www.turnpoint.net/wireless/cantennahowto.html

    ---
    Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5
  5. Archived from groups: alt.internet.wireless (More info?)

    On Mon, 13 Dec 2004 17:23:08 +0000 (UTC),
    dold@XReXXParab.usenet.us.com wrote:

    >sc.young@gmail.com wrote:
    >> So you mean that it is okay for focusing the signals that its receiving
    >> BUT the improvement in transmission is not that much. And what's the
    >
    >The reflector works in both transmit and receive.

    Not exactly. Let's go back to my light analogy. If you're receiving
    light from a distant source, all the light that bounces off the
    reflector is reflected back to the detector at the focus. This is
    good. However, if you're transmitting light, from a non-optimum
    illuminating source such as an ordinary light bulb, much of the
    "transmitted" light will end up going everywhere except to the
    reflector. If half the light goes off in some direction other than
    the reflector, you lose 3dB. My guess(tm), assuming a spherical
    radiation pattern, and a typical 0.5 f/D ratio barbeque grill dish,
    only about 1/8th of the signal (light) makes it to the dish for a loss
    of 9dB. Yes, this means that the "gain" of such an antenna is
    different in transmit and receive. You don't see different tx/rx
    specifications for commerical dish antennas because they have properly
    designed feeds, where most of the TX signal hits the dish (and uses
    the full surface area of the dish). In such cases, the difference
    between tx and rx gain is negligible.

    Read the part on reflector illumination and spillover:
    http://www.w1ghz.cx/antbook/chap4.pdf

    >There will be noise received from the "back" side of the USB dongle as well
    >as from the reflector side. Some other radiator would make more effective
    >use of the reflector. That's not to say that the reflector doesn't help.
    >The New Zealand site has some annectdotal data that says that a reflector
    >improves the connection.

    Dunno. Any kind of reflector, that redirects signal in the desired
    direction, is a good thing (as long as it doesn't cancel or interfere
    with the direct signal).

    >I don't find the USB dongle to be very omni. I
    >think it is heavily loaded toward the label side of the DLink-DWL-122.
    >That would make the reflector more helpful than if it were a good omni.

    True. Note that the DWL-122 antenna is backed by a ground plane (the
    main circuit board) and therefore has less radiation in that
    direction:
    http://www.LearnByDestroying.com/pics/wireless/DWL-122/index.html

    >To your other question, Netstumbler only shows receive signal and noise.
    >Some client programs provided with WiFi clients show "this signal" and
    >"partner signal". That would be a better evaluator of the dish.

    Yep. Don't be suprised if the received signal, when compared to the
    internal antenna or rubber ducky antenna, increases different amounts
    at each end of the link, with a reflected antenna using an inefficient
    feed.

    >I haven't used a reflector, but I have used a coffee can for a USB dongle.
    >http://www.rahul.net/dold/clarence/usb-can/im000742-800x600.jpg
    >http://www.turnpoint.net/wireless/cantennahowto.html

    I hear expresso and caffinated has more "punch" than decaf, which is
    rather inspid.

    >Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5

    --
    Jeff Liebermann jeffl@comix.santa-cruz.ca.us
    150 Felker St #D http://www.LearnByDestroying.com
    Santa Cruz CA 95060 AE6KS 831-336-2558
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