Both TV and HD radio use line-of-sight transmission. Due to the curvature of the earth, you lose reception as you get further away because you drop below the horizon to pick up the signal. The higher the antenna, the longer the reception, and then only air attenuation reduces signal strength.

A TV signal is complex and requires a LOT of power to transmit, so it dies out inside of 30 miles for the most part. Radio signals don’t require as much power, so for the same amount of power, it goes further, as long as the antenna can still be high enough to pick it up.

Because of the power drop-off for TV signals, TV antennas are most usually directional, meaning that they have great pickup in one direction at the expense of almost no pickup in the other directions. That is the reason for rotors to change antenna direction for each station. With so many more radio stations in an area, a directional antenna would be self-defeating.

Contrary to some of the (very stupid) statements in this forum, there is no such thing as a digital antenna as opposed to an analog antenna. The sole purpose of an entenna is to pick up a signal. It’s the device connected to the antenna that decodes digital or analog signals.

Part of the confusion is that some TV stations are on VHF, which requires one antenna design, while other stations are on UHF, requiring a different antenna design. Most people have both. When analog TV stops in Feb 2009, all stations will be broadcasting in UHF, so those very few people without UHF antennas will get poor reception. Eventually, as analog broadcasts shut down on VHF channels, some of the digital broadcasts will move to those vacated channels.