For the longest time I could get every OTA station from Philadelphia except NBC. I installed a rotor (rotator) yesterday and can now get NBC. The highest signal strength I can get is around 65 but I get video breakup (square blocks), picture freezes and audio dropouts. I find this strange because Fox comes in with a strength of 55 and I have no problems with the picture. I occasionally get these breakups with PBS and this is with a signal strength of 85. Will an amplifier fix this? If so, what's a good one to get?