Just a note and a warning. I, too, had the 4803 with my previous 3 LNB dish for my several HR10s. When I upgraded to the HR20s (before I knew they weren't fully functional), the installer came out and replaced my old dish with a new AT9 (5LNB with "sidecar"). He never went into my closet where the multiswitch is though.
I have since then been having intermittent satellite drop outs (actually transponders on various satellites) along with apparently good transmission. After several service calls (including one where a guy who had been out before to check on my problem merely called me in the morning and said he couldn't help me), yesterday two seemingly more proficient guys came out and tested the LNBs, the switch and the dish alignment (thanks to all here from whom I've recieved an education over the past month). They found that the main LNB was bad. Looking further, they found that one of the cables in the house side was burned from a short. They then asked what kind of switch I had when the dish was installed. I told them the powered 4803. They asked whether the guy went into the closet to unplug the switch before installing the new dish. I told them no, he never went into to switchbox.
They informed me the short likely occurred when the satellite was installed with the powered switch in place. Performance had been spotty and intermittent for about a month, including times when all satellites registered good strength, the test channels displayed properly and all channels came in fine.
I'm not sure whether this is a legitimate explanation, but I guess I'll see after about a week. If they are correct, make sure you unplug your switch before installing a new dish (or at least before installing a new AT9).
I should also say that the knowledge gleaned over the past month in this forum helped my become more proficient and enabled me to speak intelligently with the installers/service guys. Again, thanks to all.