Deus Ex Alpha

I've been having a problem with my grandma's antenna system for awhile. The signal will drop out alot, but not to the point of no signal at all. When scanning it picks up some channels but then suddenly looses them. I am about a 100km from the stations transmitter. My antenna works fine and I'm less than 1/8 of a quarter from her. The antennas are about 50-100ft from the ground. I use RG6 cable. The antenna is a Channel Master 3671, the preamp is a Channel Master 7777, and the powersupply for it is a Channel Master 0747.