Dish ant. for 802.11?

Want to use circular parabolic dish for 802.11 wireless. What simple feed can
I construct? Bi-quad looks easy. I've seen these used to feed a Primestar
single-axis parabolic ( "trough" or "slot" reflector?). Is bi-quad also good
to feed a circ. dish reflector?

Other ideas?

Thanks,
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC
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Dave,
I just did at least .4 miles thru a pine tree with 50 % signal
strength using a hawking54g with built in 6db antenna as the feed into
a direct TV dish I found in the trash. The hawking is only $50 and all
i did was tape the flat of the antenna down onto the orphaned dish amp
feed so it was oriented properly with the sweet spot. the usb adapters
also saves you the rf loss along the cable

I was testing with a laptop and the dish on top of my truck cab cradled
by ladder racks -no real optimazation - closest house .3 according to
odometer and development starts at .4 mile - I was able to pick up 4
signals by re-orienting slightly but only spent 10 minutes as I didn't
want to attract unwanted attention doing this on side of the road. I am
fairly certain I could approach 1 mile with proper mounting and
orientation and likely twice that with a second dish at the source.




DaveC wrote:
> Want to use circular parabolic dish for 802.11 wireless. What simple
feed can
> I construct? Bi-quad looks easy. I've seen these used to feed a
Primestar
> single-axis parabolic ( "trough" or "slot" reflector?). Is bi-quad
also good
> to feed a circ. dish reflector?
>
> Other ideas?
>
> Thanks,
> --
> Please, no "Go Google this" replies. I wouldn't
> ask a question here if I hadn't done that already.
>
> DaveC
> (E-Mail Removed)
> This is an invalid return address
> Please reply in the news group

On Fri, 29 Apr 2005 17:24:16 GMT, DaveC <(E-Mail Removed)> wrote:

>Want to use circular parabolic dish for 802.11 wireless. What simple feed can
>I construct? Bi-quad looks easy.

Biquad or Coffee Can feeds are fine. However, you must match your
feeds illumination pattern with the f/D ratio of the dish. Each type
of feed has a range of f/D dishes that will work efficiently. Start
reading here:
http://www.qsl.net/n1bwt/contents.htm
especially the section on feeds.

>I've seen these used to feed a Primestar
>single-axis parabolic ( "trough" or "slot" reflector?). Is bi-quad also good
>to feed a circ. dish reflector?

The biquad was designed specifically for illuminating a Primestar
offset feed dish with a f/D ratio of about 0.5 to 0.8 (depending on
axis). See:
http://www.trevormarshall.com/biquad.htm
It really doesn't matter what is the shape of the dish. It can be
oval as in the Primestar dish, square as in the Pacific Wireless
dishes, or round as in various grid and C-band converted dishes.
What's important is the f/D ratio.

Lighting up deep dishes is a problem because the feed beamwidth needs
to be rather wide. Biquads, cans, and dipoles don't do well. So,
you'll see several "scalar rings" wrapped around a waveguide or can
feed to widen the pattern.
http://www.qsl.net/ki7cx/wgfeed.htm
Also, realize that the sides of deep dishes (i.e. conveted C-band
dishes) add very little gain due to the small frontal aperature area.

If you're serious about designing and building your own, you might
wanna try modelling your dish. See:
http://www.si-list.org/swindex2.html
I suggest 4NEC2 (free) ver 5.5.0

Also note that there's a legal power limit (FCC 15.247) when using
high gain antennas (in the USA). An easy number to remember is 24dBi
gain dish has a maximum allowable +24dBm (250mwatts) tx power for a
point to point link at 2.4GHz.

>Other ideas?

Nope. You didn't bother to specify what you were trying to accomplish
and what else you have to work with. Kinda hard to guess.


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
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# (E-Mail Removed) AE6KS