I know this is old but i came on it searching for truck digital antenna advice and stungjoe is stunningly wrong.
1. The antennas operate at radically different frequencies. Some of you are way into cb's and know antenna length/shape etc make a huge difference in cb's. same in tv.
There are two "kinds" of digital antenna. One is "flat".. it's actually a crapload of pcboards with the antennas etched out so it doesnt have to rotate. A crapload of antennas in one package though small. The advantage is no rotating the antenna. The disadvantage is the small antenna size.
2. Connectors. You're going to find that a standard "tv to cable" plug (with the wires) doesnt work well. You need a higher frequency one which is easy to come by but is not the standard. The regular ones will work but you'll lose a lot of singal. This only REALLY matters if you build your own. You can build your own with a piece of wood, some coat hangers, some wire, and a booster preferably
Here is one i built once and put on my passenger seat:
MAKE | Digital TV Coat-Hanger Antenna it worked well (i hooked it to a pc tv card) with a booster
Also you can search for fractal antenna they are supposed to work well.
3. Booster. you can buy these or get one from a "digital antenna booster". They help a lot
Honestly i think im going to go sattelite. cheap dish maybe at first then one of those you mount on the qualcomm antenna mount