North Hessary Tor was originally built by the BBC as the site used to bring VHF 405-line television to much of the SW peninsula.

Its primary function today is to bring VHF FM radio to that area but this picture of  the mast shows the two small yagis [indicated by the arrow, above] which are used as the transmission aerials for the low power UHF television relay at the site. 

The UHF TV relay station serves the nearby town of Princetown and the Prison.