It could be the TV depending on Make/Model.
It could be the signal quality if you have 3 TV's of 1 aerial.
It could be a fault with the aerial cable or the connections at the end.
You will need to eliminate these possible problems before saying that the TV is faulty.
As a suggestion I would move the TV next to one with a better picture quality. Use this aerial cable to see if you are now getting a better picture. If the picture improves this will indicate that the original aerial cable needs checking.