Ultra high frequency
In Britain, UHF television began with the launch of BBC2 in 1964, using a 625-line system (which had higher resolution, and therefore required greater bandwidth, than the existing 405-line system). BBC1 and ITV soon added their own 625-line services on UHF (British channels 21 to 69), and PAL colour was introduced on UHF only in 1967– 1969. VHF was phased out by 1986. Today all British terrestrial television channels (analog and digital) are on UHF. A drawback to this is the very large number of small relay transmitters needed to fill in gaps in the main transmitters' coverage, which would not have been necessary with a VHF system due to its different propagation characteristics.