First of all, there is no such thing as a 'digital aerial'. So ignore all the marketing hype. Your best bet is to ask for a 'wide band' aerial as that will cover most eventualities. Generally speaking the more elements the better because that will give the most gain.
Then fit the aerial outdoors (Freeview often has problems with indoor or loft aerials.) and use new cable and connectors.
Start by aligning it to match the alignment of neighbours' aerials and then use a TV set tuned to a digital station and bring up the signal strength meter. Slowly move the aerial left an then right until the signal falls off by the same amount and then centre it between the two.
T
December 2009