Bruce wrote in
:

Am in the process of making a wi-fi "dual quad" antenna, two diamond
shaped lobes with the feed line and ground connected at each side at
the center.. . My question is if the actual shape of the lobes is
critical, assuming that the length of the loop is correct. In other
words, if it were two triangles instead of two squares would it make a
measurable difference?



Wrong thinking. The quad has side and rear reception. Unless you live
in a totally rural (in Bangkok??!! HA!!) area with no other interfering
signals, your enemy is other stations getting into your receiver,
crashing with your packets coming from the node. Quads are for HF,
maybe VHF to 150 Mhz as I had dual 2 meter quads up for years. Wifi is
a microwave band where microwave antennas are king. Waveguide antennas
are far better than any quad at 2.4Ghz. The N band at 5.5 Ghz is even
worse. Every time someone within 5 miles lights off a 2.450 Ghz leaky
microwave oven, your signal is trashed.

Build one of these for almost nothing:
http://www.turnpoint.net/wireless/has.html

Look at the various designs and note the gain and interference figures.
That quad would be 10 meters long in a tin shed to even come close to a
good Pringle's can with the internal flatwasher tuning to set its
bandwidth for only this band.

We're building this one:
http://www.oreillynet.com/cs/weblog/view/wlg/448
His gain measurements are very close to our observations:

Here were the average received signal and noise readings from each, in
roughly the same position:

Antenna Signal Noise
10db A: -83db -92db
10db B: -83db -92db
11db: -82db -95db
24db: -67db -102db
Pringles can
(shotgun): -78db -99db
Pringles can
(internal): -81db -98db

Here's your other enemy:

"The test partner (AP side) signal results were virtually the same.
Interestingly, even at only 0.6 mile, we saw some thermal fade effect;
as the evening turned into night, we saw about 3db gain across the board
(it had been a particularly hot day: almost 100 degrees. I don't know
what the relative humidity was, but it felt fairly dry.)"

That quad would have to be a thousand metres in the air to keep from
seeing the hot buildings and parking lots around it. Night shots are
much less noisy. At 2.4Ghz, the thermal noise is a killer.

Two 12db Pringles cans like his will connect up in flat terrain about 4
km, reliably, if there are no obstructions. Mountain top to mountain
top, 10 km is easy, maybe 15 km is possible.

It's about 1.5km between my public hotspot with a 3db omnidirectional
antenna running 200mw ERP up 10 meters inside an inverted plastic bucket
to keep the rain off my router on Channel 6, to the Pringle's antennas
on top of the enlisted barracks at the Air Force Base. Except in rain
storms, which suck up 2.4Ghz like a carbon sponge, the boys have a
nicely usable signal over that path. There isn't much interference
because I'm across the street from the base and the Air Force doesn't
trust wifi for its own stuff, of course, so that keeps them off the air.
Works great...(c;]



--
Creationism is to science what storks are to obstetrics.

Larry