Terrestrial TV
Main transmitters are horizontally polarised, so the elements should be horizontal.
Terrestrial TV is the traditional way of receiving television via an aerial. You can receive both analogue TV and digital TV (DTT, e.g. Freeview) this way. If you switch to DTT you may be able to continue using your existing aerial, but in some cases you may need to upgrade or replace it.
Types of aerial
The standard type of aerial is the Yagi aerial, which has a reflector at the back and a main rod with a number of arms or elements. The more elements the aerial has, the better it will pick up the signal.
The Yagi type of aerial is directional, so it must be pointing towards the correct transmitter. It must also be placed in the same plane of polarisation as the transmitter.
Relay transmitters are vertically polarised, so the elements should be vertical.
Aerials for digital terrestrial TV (DTT) 
Aerials in the loft
It is possible to get good reception with an aerial in the loft of your house. However, the incoming signal will be weakened by such things as roof tiles, loft insulation, water tanks, electrical cable and even the gables of the house. On the other hand, the aerial will be protected from atmospheric corrosion and so will not need to be checked as often as an outdoor aerial.
Whatever type of aerial you use, it is recommended that you use ‘satellite’ grade coaxial cable for your down-lead as this offers better reception.
Amplifiers
In some circumstances you may need an amplifier to boost the signal coming to your aerial.
Masthead amplifier
If you are in an area where the signal is weak, or you need a very long down-lead from the aerial to your TV, you may need a masthead amplifier. This is mounted near the aerial and, when fed power via the down-lead, it will boost the signal. However, if you are already experiencing ghosting or interference, boosting the signal will make these worse. Also, using a masthead amplifier to boost the signal from a distant transmitter in the presence of strong local signals may cause overloading. This is particularly likely if you are trying to boost digital signals.
Distribution amplifier
If you want to connect two or more TVs to one aerial, you can do this with a simple passive signal splitter (which halves the signal to each TV) in the aerial down-lead, as long as the signal is strong enough. If it isn’t, or if you want to connect more than two TVs to one aerial, you should use a distribution amplifier. This will split the signal and also amplify it to some extent to all of the TVs.
Distribution amplifiers are mains-powered (electricity consumption is minimal) and are designed to run continuously. Various types are available for domestic use and they can serve up to eight receivers. Some can also distribute FM radio. If you experience patterning interference when using a distribution amplifier, you may need filters.
Wideband
Wideband aerials cover all the frequencies. They do not provide as strong a signal as the single group type, but you may need a wideband aerial in order to receive digital.
DTT transmissions use the same UHF channel numbers (21–68) as analogue TV, so you can usually use the same aerial. However, some new digital transmitters broadcast channel numbers from more than one group.
In addition, when the digital switchover happens over the next few years, the channel numbers used by some transmitters may change. In either case, you may need to replace your existing aerial in order to receive DTT. We recommend the use of a CAI benchmarked wideband aerial.
If you are in a Freeview area where the signal strength is low, you may need a high-gain aerial for the best reception.
Aerial location and alignment
Whether you have analogue or digital TV, it is important that your aerial is in the best place, is pointing in the right direction, and is in good condition.
Outdoor aerials
TV signals travel in straight lines and so can be obstructed by hills and tall buildings. Ideally, your aerial should be mounted outside and as high as possible – preferably on the roof. It must be pointing in the direction of the transmitter covering your area.
Because an outdoor aerial is open to the elements, it can deteriorate and should be checked periodically. High winds or even birds can knock the aerial out of alignment, and cable connections inside the aerial junction box can become corroded. If you live near the sea, corrosion can happen quite quickly. Sunlight can make the cable become brittle, and water can also cause damage.
