Don, I didn't realize just exactly what we were working with at the time but when us folks out here in the sticks were fooling with big parabolic reflector dishes to pick up the C-band TV signals, we had two choices. High end installs used a Cassegrain feed, which consisted of a parabolic mirror mounted at the focal point of the dish. That bounced the signals down a trumpet feed horn, to the LNA that was mounted on the bottom of the dish. The other solution was something we called a Chapparral feed as pictured. This setup, complete with cob-webs and all is pictured here. The feed horns weren't all that expensive at the time, but they were just die-cast, and I gather that the GPS guys are machining their choke rings from a solid chunk of Al.

Wane is hauling old crop wheat today and dad has time to fool around while getting rich. I think I'll lash up something and see just exactly what SNRs and satellite numbers do when the antenna is tipped.

(choke ring.jpg)

(feed horn.jpg)

choke ring.jpg (60KB - 1291 downloads)

feed horn.jpg (32KB - 1284 downloads)