Simplify the following text for a Grade 12 native English-speaking person.
Original: Initial uptake of UHF television was very slow : Differing propagation characteristics between VHF and UHF meant new additional transmitters needed to be built , often at different locations to the then-established VHF sites , and generally with a larger number of relay stations to fill the greater number of gaps in coverage that came with the new band .
Simplified: 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 .