Parabolic reflector for Wi-Fi?

I've been looking to make a linear parabolic reflector for Wi-Fi, I've
found quite a few sources, such as:

http://www.genericgeek.com/index.php?q=node/280

http://www.freeantennas.com/projects...te2/index.html

Those I've found all give templates for a parabola, but without any
explanation as to why they have chosen that *particular* shaped
parabola. As a result, the drawings are a bit "sketchy".

I'd like to know a bit more theory, and the pros and cons of various
parabolic shapes.


--
Nigel M
"Occam's razor is not always sharp"

On Tue, 22 Mar 2005 18:22:57 GMT, Nigel M <(E-Mail Removed)> wrote:

>I've been looking to make a linear parabolic reflector for Wi-Fi, I've
>found quite a few sources, such as:
>
>http://www.genericgeek.com/index.php?q=node/280
>
>http://www.freeantennas.com/projects...te2/index.html
>
>Those I've found all give templates for a parabola, but without any
>explanation as to why they have chosen that *particular* shaped
>parabola. As a result, the drawings are a bit "sketchy".

For a parabola to work at maximum theoretical gain (based on aperture
size and feed efficiency), you have to be within about 1/10th of a
wavelength accuracy. That's about +/- 1.25cm. You can build it much
sloppier, but the achievable gain and pattern will suffer.

The feed is also critical as you don't want too wide a pattern
resulting in "overspray" which reduces xmit gain, or too small a
pattern that illuminates only part of the dish, resulting in low
receive gain. I short, you need to match the feed type with the f/D
ratio of the dish.

>I'd like to know a bit more theory, and the pros and cons of various
>parabolic shapes.

The best source of dish and feed info is at:
http://www.qsl.net/n1bwt/contents.htm

If you're gonna grind your own antennas, I strongly suggest you get a
modeling program. I suggest 4NEC2 ver 5.5.0 from:
http://www.si-list.org/swindex2.html

Drivel: If you just wanna improve the signal in very roughly one
direction, just chop a 5gal poly-something food bucket in half, coat
half the inside with aluminium foil, dump your access point on the
bottom, and you have an instant hemispherical reflector. Not even
close to ideal, but still useful.


--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558

Simple A4 card covered in foil and bent in the middle at 60 deg. does a good
job.
Regards,
Martin

"Nigel M" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> I've been looking to make a linear parabolic reflector for Wi-Fi, I've
> found quite a few sources, such as:
>
> http://www.genericgeek.com/index.php?q=node/280
>
> http://www.freeantennas.com/projects...te2/index.html
>
> Those I've found all give templates for a parabola, but without any
> explanation as to why they have chosen that *particular* shaped
> parabola. As a result, the drawings are a bit "sketchy".
>
> I'd like to know a bit more theory, and the pros and cons of various
> parabolic shapes.
>
>
> --
> Nigel M
> "Occam's razor is not always sharp"

Nigel

I would imagine the reflections of the signal follow the rules of optics if
you look up optics on how to focus a light bulb, I would think that's how
its done but its not necessary a parabolic reflector just convex in one
plane ( half a tube) bear in mind light reflects off a mirror at the same
angle as it hits form this you could work out what shape is ideal, but I
dont think its that critical and its not rocket science.

Please don't get stroppy but who is Occam, by the way?

MikeS

In alt.internet.wireless, MikeS wrote:

>Please don't get stroppy but who is Occam, by the way?

See: <http://en.wikipedia.org/wiki/Occam's_Razor>

My assertion is that quite often it's the more complex explanations that
are correct.


--
Nigel M
"Occam's razor is not always sharp"

Thanks Nigel,
You lean something every on the net.
Regards MikeS
"Nigel M" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> In alt.internet.wireless, MikeS wrote:
>
>>Please don't get stroppy but who is Occam, by the way?
>
> See: <http://en.wikipedia.org/wiki/Occam's_Razor>
>
> My assertion is that quite often it's the more complex explanations that
> are correct.
>
>
> --
> Nigel M
> "Occam's razor is not always sharp"