Only one channel in HD with outdoor antenna

[Michaelsccr]

I have an HDTV outdoor RCA antenna that I mounted to an old satellite dish on the roof. I am getting all local channels but the only one that is in HD is PBS. Does anyone have an idea why I can't get the other channels(ABC, CBS, FOX, NBC) in HD?

 

[americanaudiophile]

Many channels only run in HD at night during primetime. During the day they use the bandwidth for multiple SD channels.