A recent survey of my back yard revealed that I can set up a motorized 8ft dish and see from about 22W to 121W uninhibited by trees and other clutter. I unsuccessfully searched for a used dish locally, as many that are available were damaged in a severe storm over the summer. Luckily, I'm about a 1 hour drive from Sadoun and noticed that they have a nice solid 240cm steel dish for sale, called the SD2480PM.
From what I've read here and elsewhere, orthomode feedhorns are the way to go, but I'm having a bit of trouble deciding between the Chaparral Bullseye II and the Chaparral Dual Feed feedhorns. The f/D of the Sadoun dish is reported to be 0.385 whereas the feedhorns support f/D ranges of [0.39,0.42] and [0.33,0.45], respectively. So, it appears that the focal length of the dish is about 1.2cm too short for the Bullseye feedhorn to operate optimally, meaning that (I think) the feedhorn would not "see" the entire surface area of the dish.
I did some searching and came across a thread where pendragon had a similar, but more significant mismatch in f/D requirements. He was able to modify the feedhorn assembly to improve reception. I'm no stranger to doing such modifications, but I'd rather not have to do that to a $300 feedhorn right out of the box. Assuming the SD2480PM I assemble is within spec, should I not be concerned about this difference in f/D and get a Bullseye or just play it safe and get the Dual Feed?
I should add that I have a 1m Primestar dish on an SG2100 elsewhere in the yard for Ku reception, but it's currently limited to seeing 61W to 127W. I'd like to pick up Ku on the 8 footer since it will see the Atlantic birds better, it's convenient, and I'd feed the output from it into a TBS 6925 (for playing with 16APSK and 32APSK feeds; the feasibility of doing so in C band from an 8ft dish is probably a topic for another thread) while running the Primestar off a Prof 8000.
From what I've read here and elsewhere, orthomode feedhorns are the way to go, but I'm having a bit of trouble deciding between the Chaparral Bullseye II and the Chaparral Dual Feed feedhorns. The f/D of the Sadoun dish is reported to be 0.385 whereas the feedhorns support f/D ranges of [0.39,0.42] and [0.33,0.45], respectively. So, it appears that the focal length of the dish is about 1.2cm too short for the Bullseye feedhorn to operate optimally, meaning that (I think) the feedhorn would not "see" the entire surface area of the dish.
I did some searching and came across a thread where pendragon had a similar, but more significant mismatch in f/D requirements. He was able to modify the feedhorn assembly to improve reception. I'm no stranger to doing such modifications, but I'd rather not have to do that to a $300 feedhorn right out of the box. Assuming the SD2480PM I assemble is within spec, should I not be concerned about this difference in f/D and get a Bullseye or just play it safe and get the Dual Feed?
I should add that I have a 1m Primestar dish on an SG2100 elsewhere in the yard for Ku reception, but it's currently limited to seeing 61W to 127W. I'd like to pick up Ku on the 8 footer since it will see the Atlantic birds better, it's convenient, and I'd feed the output from it into a TBS 6925 (for playing with 16APSK and 32APSK feeds; the feasibility of doing so in C band from an 8ft dish is probably a topic for another thread) while running the Primestar off a Prof 8000.
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