I've been running an ADL dual orthomode feed for the past few months on my 3 m Winegard Pinnacle. The f/D of this dish is 0.278, which is great for pulling in low SNRs, but unfortunately the ADL orthomode is a poor match out of the box. Patriot now sells this model, and according to their website, the feed is supposed to work over a f/D range of 0.300-0.365. I did some rough calculations a few months back, and the low end of their range seemed highly optimistic. With the scalar ring shoved as far up as possible, I measure the feed opening projecting only 0.8 cm beyond the scalar rings. On a deep dish like the Winegard, this is going to cause the feed to illuminate only a center section of the reflector.
I designed a new scalar-like interface for the feed, but I've been too busy to fabricate it. So yesterday I decided to try an intermediate solution by cutting out the portions of the scalar ring that were preventing the ring from being moved further up the feed. I had to saw out sections of the clamping ring to make room for the C-band ports off the feed, and slice two sections out of the scalar rings themselves. With a bit of filing on a couple of ridges inside the clamp, I was able to move the scalar so 2.3 cm of the feed now projects beyond the rings.
This made a substantial improvement in performance. For SQ counters, this bumped up some of high SR transponders by 10-15 percentage points. I made some rough measurements, and believe I'm seeing about a 1-2 dB improvement in most of my SNRs. That's a big deal.
I should also mention that this feed seems to really like the focal point of the dish about 1.2-1.5 cm inside the feedhorn. That's a bit more than I expected. I don't have a Chaparral dual ortho, but on the surface the pictures look pretty close to the ADL, so this mod may also apply to that feed.
I've attached a couple of photos that show (1) the cut-outs on the scalar rings and (2) the portions of the clamping ring that had to be removed. The last picture also shows some beer can shims I added to prevent the scalar from 'walking' when it is being tightened.
I designed a new scalar-like interface for the feed, but I've been too busy to fabricate it. So yesterday I decided to try an intermediate solution by cutting out the portions of the scalar ring that were preventing the ring from being moved further up the feed. I had to saw out sections of the clamping ring to make room for the C-band ports off the feed, and slice two sections out of the scalar rings themselves. With a bit of filing on a couple of ridges inside the clamp, I was able to move the scalar so 2.3 cm of the feed now projects beyond the rings.
This made a substantial improvement in performance. For SQ counters, this bumped up some of high SR transponders by 10-15 percentage points. I made some rough measurements, and believe I'm seeing about a 1-2 dB improvement in most of my SNRs. That's a big deal.
I should also mention that this feed seems to really like the focal point of the dish about 1.2-1.5 cm inside the feedhorn. That's a bit more than I expected. I don't have a Chaparral dual ortho, but on the surface the pictures look pretty close to the ADL, so this mod may also apply to that feed.
I've attached a couple of photos that show (1) the cut-outs on the scalar rings and (2) the portions of the clamping ring that had to be removed. The last picture also shows some beer can shims I added to prevent the scalar from 'walking' when it is being tightened.