my hr10-250 gets a steady signal 90 on WLBT (frequency 9) no drops, large outside uhf/vhf rca antenna about 15ft high, no amp or preamp, out in brandon.
have not seen any true HD from them yet tho signal is full power and audio is fine.
no clue if it would work for you but a guy in the hdtivo forums claimed he used a FM trap ($6 at radio shack) to cure his ota signal drop problems. some amps, preamps come with a fm trap may have a switch on it to turn it on/off.