My USB Digital TV Tuner cannot be used in a moving car due to Digital TV signals not working well at speeds over about 60km/h, but have no fear! Elgato is here!
This device has two integrated receivers and two portable antennas, which is great for low signal locations and speeds at up to 160km/h!!! And it's made for the Mac too! :)
EyeTV Diversity Dual-Tuner DVB-T Stick