If you are receiving analogue television from across the border in Northern Ireland (BBC1, BBC2, UTV, Channel 4, possible Five in a few places), you should be aware (if you're not already) that these transmissions will cease in about two years time (at the time of writing, shutdown likely to be the second half of 2012) to be replaced with high-powered digital services, known in the UK as Freeview.
The question then lies as to if the current aerial pointing into the North will be good enough? Fortunately there is a "rough" test that was developed by engineers at BBC Research & Development using teletext to see if your current aerial should be suitable after the analogue signals are closed down.
As of this moment, none of the main transmitters in the North nor any of its relays except one should require a new aerial installation for this switch over although some of the relays are moving to new frequencies within the same aerial group (Kilkeel and Gortnalee are two that may affect viewers in the Republic), so to test wherever your analogue reception is strong enough to receive at least some DTT services from N.I. after the analogue signals are terminated, do the following...
*** Please note, this test is no good if your analogue signals are coming from a "deflector" ***