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LNB For KU AOR Dish (Project)

I put this in the C band section due to the dish being a prime focus.
Over the years I've been playing with different configurations for my KU Atlantic Ocean Region dish. It is an 8 ft Channel Master SMC with left hand drive that can cover 12.5W to around 103W. In the past I have used an Invacom TWF-031 with an Invacom C120 prime focus feed. The configuration worked quite well but with only 2 outputs it could only work with 2 dedicated receivers, and I had a couple others that I wanted to have connected. I then tried a double ortho configuration with a set of low band and a set of high band LNB's. That worked well, but I became irritated with having 2 different dish positions for each band.

The last year or so I've been looking around the European forums, and the talk of the town has been the Inverto Black Ultra as the amplifier of choice for weak signals. Before burying my bundle of wires last year I made sure it contained 4 coax lines for that dish, so a quattro with separate outputs for each band/polarity seemed to be the thing to do. I have a pretty big power supply so I don't need built in voltage polarity switching...that will be done with the multiswitch.

The problem I then faced was the Inverto didn't come in a C120 flange version and I wanted to use the Invacom prime focus feed I had handy. So how could the Inverto be converted to prime focus? It was evident the offset feed would need to be chopped off, thereby voiding the warranty. We experimenters always have to take a chance I guess. My first thought was to cut off the offset feed and not use a flange at all and just mate the waveguides together somehow. That was going to be the plan until I considered having a machinist cut the offset feed off, then turn and thread the waveguide to accept the threads from the prime focus scalar. There would be less waveguide loss that way.

The conversion was successful and preliminary testing is very encouraging. I have to extend the mounting screws on the feed support as I'm still about 0.6" too long on the focal length but signals are great even with the long focal length.

Pic 1 is the naked LNBF with a cut mark applied to mark where to cut the offset scalar. Pic 2 is the scalar cut off and the waveguide turned and threaded. Pic 3 is the LNBF with the Invacom prime focus scalar attached. Pic 4 and 5 are of the installation after bringing the focal length to the required 38.5".


After today's tweaking...
My test satellite is the signals on the Spot 2 beam of Intelsat 903 at 34.5W. This beam is aimed to the Eastern Caribbean and Northern South America. I'm WELL to the North of this beam, and even 1Captain (who reports most of the signals on this satellite) is just on the edge of the footprint. Before, I could only lock 2 of the signals and they both had errors. Now I can lock every signal on that beam with the exception of a single data signal, and I'm not even sure my receiver could lock it anyway. All signals are error free. I'm extremely pleased with the results.