The answer to this question is not quite as straightforward as you might think. The number of systems you can legally use is determined by the availability of licences (see the next question).
Technically, in the VHF band, there are between 15 - 20 frequencies you could use, but remember that there is a lot of traffic in the VHF band, and the more systems you use, the more likly it is that you will encounter interference.

The UHF band is split into TV channels 21 - 69. This is because a TV station needs a whole channel to transmit vision and audio. Channel 69 is reserved for low power (i.e. radio mic) use and is available across the UK. Channels 61 to 68 are generally available but there are some restrictions to its use, and can only be used once you have applied for a license through jfmg, who, on behalf of OfCom, organise frequency allocation for the whole of the UK.

Systems differ in the number of systems they can squeeze into a single TV band

Because of intermod interference, if you are using all the frequencies in one channel, you will not be able to use all the frequencies in the adjacent bands - for example, with the Trantec S4000's, if 69 is fully used, you can get 6 frequencies in Ch68 giving a total of 20.


You could also use UHF and VHF systems together.