analog will look grainy compared to digital.
Not really. Analog won't be as clear/sharp as digital, the grain comes from poor signal level/quality.
The OP has the same results on both his HDTV and his SDTV. He wants to know if his "HD" antenna is the cause. Nobody here has straightened him out about HD antennas and I am surprised.
ELMWOOD, There is no such thing as a 'HD' antenna. There are only UHF & VHF antennas and has been that way for the last 50+ years. The tern 'HD' was added to sell antennas only, otherwise known as marketing hype.
The reason for the one channel being so grainy, ergo such a lousy signal, is simple. The ONLY way a station can remain analog in the United States today, is if it is a LOW POWER station. This is because they generally have such a low viewership that they cannot afford to convert to digital. The only way to get decent reception is for you to get a better antenna, a pre-amp or move closer to their tower.
Usually, you can watch CBC or CBC type programming on another channel that is digital. Depending on your location of course. You can also subscribe to cable or satellite, or even get your own C &/or Ku band satellite dish and receiver and get more religious stations for free than you will be able to use.
Hope this explains enough for you. If not then feel free to come back and ask more questions and we will try to be of some help for you.