Freeview channels are transmitted alongside the normal TV signals from your local TV transmitter mast. Although many traditional analogue TV transmissions can be received using a set-top aerial, these are ineffective when trying to receive digital Freeview signals; a rooftop aerial is usually required. To obtain the best possible reception, the aerial must not only be aligned to point at the strongest local transmitter but must also take into account the polarity of the transmitter signal.
Establish the location and polarity of the strongest local transmitter delivering Freeview. Enter your Post Code or Ordnance Survey grid reference on the UK digital TV reception predictor webpage to obtain this information. Alternatively, observe the direction of other aerials in your area and note the most common compass bearing.
Check the suitability of your aerial by visiting Teletext page 284. This service is provided by the BBC and checks the suitability of your aerial for Freeview reception.
Mount the aerial with the correct polarity to receive the strongest Freeview signal. Signal polarity is either horizontal or vertical. Rotate the aerial so the elements are vertical to match with a vertical polarity signal and horizontal to match with a horizontal polarity signal.
Align the aerial using the compass bearing obtained in Step 1. Initially align the aerial to match the alignment of the aerials on adjacent buildings and use a compass to fine tune the alignment.
Connect the aerial to a television set and tune to either BBC1 or ITV 1. Make minor adjustments to the direction in which the aerial points until the strongest signals are found for these two stations.
Tie the compass to a length of string and hang it around your neck. Dropping a compass off a roof is bad for the compass and bad for anyone underneath it, and retrieving it is time consuming.
If, after correctly aligning the aerial, you cannot receive a good Freeview signal, check the grouping of your aerial. Ensure that it matches the group of the local transmitter. Aerials are designed to receive particular groups of signals, and sometimes tuning fails because the aerial cannot receive the frequency transmitted by the local transmitter.
Working on a rooftop is potentially dangerous. Wear suitable clothing and personal protective equipment.
If you use a ladder, get a friend to guard it and stabilize it while you ascend and descend.