In alt.internet.wireless DaveC wrote:
Working with 2.4 GHz 802.11b wireless signal. Using USB adapter (one of those
thumb-sized products) and an old 18-inch satellite TV dish.
With a circular, symmetrical parabolic dish, I presume that the focus is
directly above the center. I've located the tiny antenna within the adapter
as close to this point as i can.
Oops. It's not circular or symmetric.
I've heard that it is a portion of a parabola, rather than a parabola in
itself, as if the oringal mounting point of the LNB were mounted in the
predicted focal point of a larger piece of metal that did form a parabola.
The proper focal point is wherever the antenna element was on the original
LNB. The frequency doesn't matter. That's still the focal point.
The next problem is knowing exactly where the antenna is in your USB
widget, so that you can put it in the same spot.
( Odd thing about this dish -- this one is a DishTV brand -- is that in the
original design for satellite reception, the driven element [ the "can", the
input to the LMB ] was located low on the dish. In other words, the focus
used in this design was off-center, about 30 degrees below the center axis of
the dish. This would mean that aiming would be off-axis, too, yes? What is
the reasoning behind this design? )
I think it's 22 degrees, but it is certainly "off". The old Primestar
dishes often looked like they were pointing at the ground, instead of into
the heavens.
I tried rotating the dish on its axis to account for polarity mismatch (
would this really be an issue? ). No joy.
My DLink DWL-122 USB adapter improves noticeably when the orientation is
correct. I tried the face facing the WAP, horizontal and vertical, as
well as edge on, horizontal and vertical. I didn't try end-on.
For my setup the face on - horizontal was best.
The wireless adapter can receive signals well, generally, w/o a dish, but
because of my location, reception of the desired signal is not great.
I put my USB widget 1" in front of a 9" pie tin. The 9" pie tin isn't
really quite large enough. 1" was discovered empirically, and appears to
be good for about 6db, according to Netstumbler. It is also far more
stable with the pie tin, where without it the signal seems to wander.
http://www.usbwifi.orcon.net.nz
His wok is a parabola. That doesn't count for you.
I was going to use a reflector like Trevor's BiQuad to feed the USB to a
Dish-Dish, but my son cleaned out his garage and threw the dish away about
a week before I asked for the dish ;-(.
I think the reflector behind the USB widget, painting a parabola, should be
a good combination. And the right focal point for the odd-shaped Dish-dish
is important.
http://www.trevormarshall.com/biquad.htm
http://martybugs.net/wireless/biquad/
http://63.142.46.238/buck/CantennaUSB.html
And my favorite site:
http://www.nodomainname.co.uk/cantenna/cantenna.htm
Where David uses a full sized USB adapter, pulling the antenna loose and
sticking it through the side of a can.
I might put my mini-usb inside a can.
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Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5