Originally Posted by Tim Deegan
Following on from what fudge said. You do need a far better signal from your aerial to receive digital. So you may need a better aerial.
Not entirely true...
If you had a good analogue signal then there's no reason as to why you couldn't get a good digital signal. Digital signals though tend to be more spread on the spectrum so sometimes a more wideband antenna is needed.
Try this website
as it'll tell you if you're in a fringe area and you can compare the details in the analogue predictor with the digital predictor.