You don't need the pre-amp to block FM. You can purchase a FM trap for around five bucks from
www.solidsignals.com Also FM typically only effects VHF (2-13). Your channel 7 is working fine on your UHF antenna, so unless you are having problems with a real not vurtual VHF, FM is not your problem. If you want to try an amplifier for the stations to your East, try the 7778 amplifier, not the 7777. You may experence overload from the strong signals from nearby local channels.