If you are using the same aerial for digital TV that you used for analogue TV it is quite possible that the aerial is the problem, especially if you have NEVER been able to receive these channels on your digital TV even though the analogue TV did receive them.
If you have a 'grouped' aerial you may need to have it changed for a 'wideband' aerial.
Seek the advice of a LOCAL aerial company as they will be aware of the characteristics of your local transmitters.
Good luck
Lee
November 2007