DaveC wrote:
On Sat, 4 Jun 2005 06:15:39 -0700, Russ Renaud wrote
(in article ):


W1GHZ has an application that will determine the focus of your dish for you.


I know the focus of the dish. Just need to know the point used as the feed
point.


Now you just have to figure out where the phase centre of your feed is...


It sounds like it is the entrance to the throat of the (original) guide where
the guide connects to the horn. According to this, you can lengthen or
shorten the guide at that point to change the "depth of radiation" (whether
the feed illuminates a small or large diameter of the dish), according to:

http://tinyurl.com/ar9es

I guess I wasn't able to divine your intent, then.

You say you have a surplus DirecTV "feed". You say you know the focal
point of your dish. You want to use your own 2.4 GHz feed. You
make mention of an adjustable feed - is it a chapparel-type feed because
I didn't think the DirecTV feeds are adjustable?

What kind of horn are you planning to use for 2.4 GHz? DirecTV dishes
are usually fairly small - the more efficient feedhorns are fairly
large, at least for 2.4 GHz if you have a .7 f/D DirecTV dish.

The simple answer is to place the phase center of your 2.4 GHz feed at
the focal point of your dish. What is the phase center of your 2.4 GHz
feed? Maybe this is the question you want to ask. If so, the answer is
probably here.

http://www.qsl.net/n1bwt/contents.htm