Archived from groups: alt.internet.wireless (
More info?)
What kind of gain could one expect from this type of antenna ?
Also in playing around with this particular model of USB adapter I was
less than impressed with performance as opposed to other actually less
well known brands.
Any idea of the chipset used on this D-Link USB adapter ?
Jeff Liebermann wrote:
> On Sat, 20 Aug 2005 16:12:13 +0000 (UTC),
> dold@XReXXTryin.usenet.us.com wrote:
>
> >yahikochan1 <yahikochan1@gmail.com> wrote:
> >
> >> from the links all give me i will read it, but i notice that in one of
> >> the antenna was at 10 angle of elevation i keep mine on 20 that could
> >> be a a big error.
>
> >I have seen diagrams of the DSS offset dishes that show the true aim on the
> >web. I remember someone stating that they weren't a parabola, but a
> >portion of a parabola, so that they didn't point where they appeared to be
> >pointing. I recall that Primestar dishes always seemed to be pointed at
> >the ground when they were pointed at the satellites.
>
> The common offset feed vertically eliptical DBS dish has an
> interesting geometry. If you look at the dish from the focus, it
> appears to be a perfect circle of about 18" in diameter.
>
> The dual LNB horizontally oval dishes, that are about twice as wide as
> they are high, are the equivalent of two 18" dishes side by side. The
> reflection from the left LNB goes to the opposite (right) side of the
> dish. The other side of the dish contributes nothing to the gain.
> This is necessary to prevent a "daisy" antenna pattern, which will
> pickup spurious rubbish from other satellites.
>
> The less radically oval DBS dish antennas with dual or triple LNB
> feeds are a compromise between gain and beamwidth. The design goal is
> to keep the beamwidth from both LNB's around 2-3 degrees, while the
> antenna is pointed in the same general direction. If you look at the
> patterns for dual and triple LNB systems, the 3dB beamwidths are all
> around 3-4 degress, but the 10dB beamwidth (an indication of side
> lobes) goes from 3-4 degrees for a single LNB, to perhaps 7 degrees
> for a triple LNB. It's not a perfect parabola but a good compromise.
>
> Note that all this is for 10-13Ghz. The single LNB dish will probably
> work at 2.4Ghz, but methinks the parabola is far too distorted with
> the dual and triple dish designs to insure that the phase center is at
> one point at 2.4Ghz. I might be wrong, but I'm too lazy to run the
> models to be sure.
>
> >The indicator on the mast of my DirecTV dish is calibrated for the true aim
> >when mounted to a vertical pole. If you have yours pointing at 20, that's
> >a long ways off from directly horizontal, and this is a very narrow
> >beamwidth. You might move it around while trying to point at a WAP that
> >you can see easily.
>
> There are lots of ways to aim an offset dish. I do a test adjustment
> to get the vertical elevation exactly horizontal when mounted on a
> perfectly vertical pipe. I can then just spin the dish around to
> wherever it's suppose to point and not worry much about vertical
> alignment.
>
> >If the surface of the dish is optically reflective, you could point it at
> >the sun and see the reflection on the feedhorn.
>
> Ummm... Melted USB dongle perhaps? You could temporarily cover the
> dish with aluminium foil and do this experiment. However, I'm not
> sure I would want to be at the focus when you try it.
>
>
> --
> Jeff Liebermann jeffl@comix.santa-cruz.ca.us
> 150 Felker St #D
http://www.LearnByDestroying.com
> Santa Cruz CA 95060
http://802.11junk.com
> AE6KS 831-336-2558
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