"John Ferrell" wrote in message
...
On Thu, 26 Jun 2008 07:35:31 -0500, "amdx" wrote:

I have a Directv dish 35 inches wide x 20 inches tall 4inches deep.
I calculated the focus as F=D*2 / 16d where D =diameter and d=depth
F=18 inches Ok so far.
How do you find beamwidth? I think the 35" dimensiom would have a tighter
pattern than the 20 ", but how do you calculate,

Second, The feed antenna, There can be different feeds.
A simple monopole, dipole, biquad, patch, yagi, helix.
How does the feed antenna affect the gain of the dish, if at all?
Yea, it my be difficult to light the yagi or helix, so if you like throw
those out.
Thank You,
Mike

You have a neat gadget here!
If you place a lamp (flashlight?) at the focus you can measure the
beam on a wall wth a tape measure.

It grey, won't reflect light very well. Basically I wanted to know how the
beamwidth changed with the larger width dimension vs the smaller height
dimension

Put a microphone at the focus and you can hear things you would not
believe...

I already experienced the reflection. I had a radio playing on my right
side, I was moving the dish and got an increase in volume in my left ear. I
moved the dish back
to play around with the effect. Neat!

Old ARRL antenna books, and authors like John Krause will be needed
to answer all of your questions.

John Ferrell W8CCW
Beware of the dopeler effect (pronounced dope-ler).
That's where bad ideas seem good if they come at you
fast enough.