Ok, I have DISH HD. I am using the RCA off air attic antenna, I can receive ABC CBS, NBC channels in the daylight hours with a 80-88% signal strength... VERY GOOD, BUT at night, CBS and FOX drop off dramatically regularly dumping the signal... SO figuring that I need to Amplify the channels, I added a LEVITON video amp. 5mhz-1000mhz. NOW ALL OFF AIR channels are 50-55 which means NO HD. I have disconnected the AMP and looking for answers.
You should also look at how you've setup your antenna (direction and distance). You should use antennaweb.org to do this.
How long is your cable run? You should look at a Pre-amplifier (hooked up close to the antenna) if you have a long cable run over 75' to 100'. Pre-amplifiers are designed for OTA antennas where there is a long cable run and are different than an amplifier.
Here's some information on Pre-Amplifiers that I referenced from Stark Electronics:
Pre-Amplifiers
A Pre-Amplifier (pre-amp) is a mast or antenna mounted amplifier used primarily to eliminate "snow" on the TV screen. Snow is actually electrical noise that is generated by the TV receiver and other electrical devices. The objective of any antenna installation is to deliver enough signal to the TV set to override the noise (snow). A "weak" signal is one that is not strong enough to override the level of the noise in the set. Another obstacle is the signal loss incurred while traveling through the transmission line connecting the antenna to the TV set. An antenna that has acceptable gain at the antenna tapoffs but encounters excessive loss due to long cable runs will also deliver a "snowy" picture to the TV set due to not enough signal makes it to the set to override the noise level. A pre-amp would be used to compensate for the losses in the transmission line as well as the noise level of the set.
All pre-amps have a power supply that plugs into an AC outlet inside the house that lowers the voltage and sends it up the coax to power the amplifier which is mounted up near the antenna. The benefit is that you get amplification before any line loss or noise and you don't have to run 117 AC up to your roof. NOTE: Don't install a regular splitter between the power supply and the pre-amp or you will short circuit the system and it won't work. You can install a special splitter that is power passive on only one port. Or put a DC Block on the outputs that don't run to the power supply. Also you can't put any type of matching transformers between the power supply and the pre-amp.