Here's a tip. Construct a Tee piece say 2 inch across the top of the tee. Emanating at a 90 degree angle from the center of this 2
inch piece is a straight edge long enough to reach and pass the theoretical focal point....make an educated guess....Mark the
center of the parabolic dish with a magic marker. Use a tape measure or fasten a rod of any material perpendicular to the dish
center. Place the Tee piece anywhere on the surface of the dish and where the leg of the Tee crosses the center rod is the focal
point. Do this several times from different locations on the dish surface and average the crossing point on the perpendicular.
Simple.
Steve

"Bruce" wrote in message ...
On Tue, 20 Apr 2010 09:07:53 +0200, "Steve Lusardi"
wrote:

Bruce,
I assume you know how to find the parabola's focal point. I won't bore you with a plan if you already know. Let me know if my
assumption is incorrect.
Steve


Yes, have the formula and know about the reflected sunlight method,
although that never seemed to work for me as when I put out a piece of
paper to measure the reflection it shaded the dish and the reflected
beam was too weak to see :-) I'll have to get a special piece of
something transparent to use.


"Bruce" wrote in message ...
On Mon, 19 Apr 2010 22:28:25 +0200, "Steve Lusardi"
wrote:

As I stated Bruce, the TV antenna is a good plan. It will be a true parabola and the gain over what you have will be
significant.
Don't forget about the 30 degree included angle that is built in. You will have to move the detector up to the center for your
application.
Steve


No worry about misalignment a there is no "horn" on it. Just a dish
:-)
It is currently being used as a "roof" for a well pump and I have some
20 ltr. pails that, with a notch cut in one side to clear the piping
will work even better so I reckon a trade can be made... once I and
them get back to Phuket.

"Bruce" wrote in message ...

I ended up building two wi-fi parabolic antenna. the first a 300 mm
screen-wire dipper (used for frying bananas) measured 300 mm in
diameter and about 90 mm deep. Later built a second dish using a 430
mm aluminum "wok" about 100 mm deep.

The first antenna gave a better signal then the adapter but the second
antenna gave, using the instruments available to me, approximately 3
times the signal that the bare wi-fi "adapter" had.

As I previously mentioned I do not have a signal strength meter and
used the standard Linux utility "iwconfig" to produce some sort of
data. It gave a reading of 6 for signal strength using the bare
adapter and as high as 23 with the wok I can only assume that whatever
the value of the increments that the ratio is accurate.

As luck would have it, I found an abandoned TV "cable" antenna - as
used here "cable" is received on a 3 foot dia. parabolic antenna and I
will probably try that at some later date.

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)
Cheers,

Bruce
(bruceinbangkokatgmaildotcom)
Cheers,

Bruce
(bruceinbangkokatgmaildotcom)