[wejones]

Yeah, it could very well be a polarity thing, which if there are no interferring channels, won't affect reception that much, but with polarity off, some channels will have interferrence, and be affected more than others. It could be that in order to improve quality on one strong channel, that the dish had to be moved off the sat to avoid interferrence from nearby sats, enough to kill reception on the weak channels. I also have to ask, whether the focal length was carefully measured when installing the LNBF? If the focal length is off, you can be receiving 2 sats at once. I once used to peak my dish on one sat, and would try to get a weak transponder that I knew was on that sat, but instead, I'd get a transponder from a nearby sat instead. I'd have to move the dish a bit to pick up the weak transponder. Thing would go blink, and kick over from the wrong signal to the right signal. That was an unusual situation with 2 signals with exactly the same parameters, but it shows how you can get interferrence from nearby sats if the polarity is off, or due to the poor resolution of a smaller dish, or in my case contributed to by sidelobes, etc.