I have two Zenith 520's. Get the same signal strenghth on Sat. A & very close on Sat. C. But the signal strentgth varies 6-7 points on Sat. B, especially on Tr. 25. I went up on the roof yesterday and switched the cables on the multiswitch. The difference remained. The difference on Tr. 23 is only a couple of points. VERY STRANGE!