On Wed, 23 Jun 2010 16:53:55 +0000, Larry wrote:

Bruce in Bangkok wrote in
:

However, the recommended length of the "Cantenna" seems to be one wave
length. Which is about 8 inches. Because of what I welded together to
make the tube mine ended up 12 inches long, about 1.5 wave length. Dom
you think cutting the tube to 1 wave length improve signal strength?

Anything over a wavelength doesn't increase the directivity much from our
experience. We did get more signal by adding a cone to the end, about a 45
degree angle out to a larger feedhorn to collect the signal. It also
reduced our sidelobe. I'm not sure it really made any difference in signal
quality, though. The sun noise bouncing around all over gets in the tube,
anyways, some.


Secondly, I am now getting greedy. Since the Cantenna and the dish
each worked very well, thank you, I'm now thinking of combining the
two. If I do that I am assuming that the mouth of the tube should be
at the focus point of the dish? right?



That would be fun to try. Make the mount out of stiff wire so you can play
with bending the mount to adjust the position of the cantenna. ANYTHING
you do to collect the signal and concentrate it on the antenna really makes
a difference. Notice how huge commercial satellite antenna dishes are?
The bigger the better because it is like a big telescope mirror, collecting
and focusing more signal on the detector.....

http://www.astro.cornell.edu/academi.../ao_scheme.htm
(The ultimate collector)

Got a 36 inch dish given to me today. Am planning on making a mount
for a cantenna and see how that goes. I think if I paint it with
flowers, or something, my wife will let me keep it in the room - if it
doesn't block the wind coming in through the window :-)

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)