From: Jeffrey Lomicka <JeffreyLomicka-AT-comcast.net>
Date: 03 Jul 2009 05:28:12 UTC   (08:28:12 AM in author's locale)
To: xtensionlist-AT-shed.com

According to site I used to construct my reflector, frequency wasn't an
issue, the site says " This reflector is frequency independent, meaning
it will work with any wireless gear on any band."

However, the Electrical Engineer in me has two thoughts on this. My
first thought is that reception would be best if the reflected signal
was in phase with the direct signal, meaning you want a distance of
about a 1/4 wavelength or 3/4 wavelength, but my second thought is that
the reflector collects so much more signal than the direct that the
additive contribution of phase alignment may not be relevant.

>From a practical standpoint, it worked well at WiFi frequencies, but did
nothing for me on UHF DTV. Come to think of it, 310Mhz is in closer to
the DTV range than the WiFi range, so this might not be helpful at X10
frequencies.

I found a web site to do the math:
eosweb.larc.nasa.gov/EDDOCS/wavelength.html

1/4 wave at 310Mhz is 24.25cm.
1/4 wave at 455 Mhz is 16.5cm
1/4 wave at 2.5Ghz WiFi frequencies is 3cm

Hmm, I scaled up my reflector thinking bigger is better, but I should
build a smaller one with 3cm figure in mind and see if it works better.

One caveat, in college, I failed both Electromagnetic Fields and Waves
and Communications, so I'm clearly the wrong one to ask about RF issues.

- Jeff

Doug Kiekow wrote:
> Jeff,
> I've installed whip antennas on some wireless stuff, would like to try
> a parabolic reflector on the whip, but am given to understand the
> dimension from the whip to the reflector is critical. Is that correct,
> and if so how do I find out the gap?
> dougy
>
> On Jul 2, 2009, at 8:31 AM, Jeffrey Lomicka wrote:
>
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