On Sat, Jun 15, 2002 at 10:01:59AM -0400, bryan mcdade wrote:
> I was looking at the home-brew antenna shootout, located at : <
> http://www.turnpoint.net/wireless/has.html>. Could someone explain to me
> why channel 1 had better signal then 5 or 11. I had always thought that
> you should get the same (or close) signal strengths on any non-overlapping
> channel (1, 6, 11), provided that the noise is the same (lab environment).
> Based on this test it seemed that channel 1 constantly has better
> reception.
There can be a couple of factors. The one I can say that will have
a very slight impact is free-space loss is less at lower frequencies,
but that only accounts for 0.1782 dB difference of free space loss
between channel 1 and 11.
Another factor could be how the antennas are tuned. They may all
be inadvertently designed to center on a channel lower than channel
5 or 6.
One more factor could be how their test set up is not the most
"factory". They could have problems with their receive set up
favoring the low band due to the antenna, coax length (standing
wave issues), reflections (muti-path), etc.
As I really can't see their setup being much more accurate than +/-
3 dB I would say it is more likely the last explanation. Keep in
mind the difference between channel 1, 5 and 11 that they show is
usually between 2 and 3 dB (+/- 1 to 1.5 dB). I wouldn't put too
much credit into this effort unless it was done with calibrated
equipment, an anechoic chamber or properly designed open-range,
etc..
Tim
--
Snail: Tim Pozar / LNS / 1978 45th Ave / San Francisco CA 94116 / USA
POTS: +1 415 665 3790 Radio: KC6GNJ / KAE6247
"It's a damn poor mind that can only think of one way to spell a word."
- Andrew Jackson
"What is wanted is not the will to believe, but the will to find out,
which is the exact opposite." - Bertrand Russell, "Skeptical_Essays"
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