WHEN they were available, the RP-1 series of feedhorns from ADL was much better than Chaparral in performance. I can honestly say that I have never had a situation in which the proper model of ADL feed (RP-1 or RP-2) could not make a significant improvement over an existing installation with a Chaparral.
What I did find in my many years with Orbitron was that many satellite dealers had no clue about properly installing feedhorns. An adjustable scalar such as the Chaparral PR1E, Corotor 2 or ADL RP-3 might allow them to get away with breaking the rules, but when using a FIXED non-adjustable feed such as the
ADL RP-1 and RP-2, many complained about poor results. Rule number one is
to set the F/D ratio on your feed for the antenna being used. In the case of the
RP-1 or RP-2, that was non adjustable. The RP-1 was designed for 0.335 to 0.425 f/d ratios, with the RP-2 specializing in 0.275 to 0.335. It was also about 7/8 inch thicker in the feed plate, so that had to be compensated for. The next step is to
install and adjust the focal length properly. The Orbitron devised solution was to
install four 3-inch slotted round-head machine bolts and 12 1/4 inch nuts.
Push the machine bolts through the feed plate, spin and wrench tight one set
of nuts on the back of the feedhorn. Spin another nut onto each of these "legs"
Install this assembly into the Quad Legs, and spin the last nut on back side to secure the feed. Now, carefully adjust the middle nut with your fingers for the
proper focal length and wrench the last nut tight to secure.
The biggest stupid installer mistake was in simply bolting on a feedhorn scalar
plate to the quad legs, and adjusting the movable center part in and out for
best signal. This bad habit blinded their minds to the concept of first adjusting
the f/d ratio, and using the quad legs (with or without external adjusters) to
get the focal point perfected. While one may find the hot spot of the focal point,
unless the f/d ratio is set properly on the feedhorn, precious signal will be lost due to a mismatch with the antenna.