History
Typical of a mid-1960s site with "standard tower", Thornhill was an existing Repeater Station for cables to Southampton. The site now has housing immediately adjacent which seems to have been developed around the same time as the Radio Station. Thornhill was developed as part of a new route linking London with Rowridge and Southampton, replacing the 1950s link via Golden Pot. We understand an interim arrangement was in place by 1966 to allow BBC2 to transmit from Rowidge. ITV and BBC1 did not start UHF service from Rowridge until December 1969 - this is understood to have been due to delays with the site at Bagshot. It is unlikely any telephony links were operational before 1970. The original installation used "small" horns facing Butser Hill but dishes towards Rowridge, these being mounted at approximately 45 degrees to the tower. Large dishes were still present on this alignment in 2016 and Ofcom data shows a 6 GHz link betwen Thornhill and Rowridge is still licenced.
Television links were more extensive than would first appear - Southern Television had their main studio at Southampton and the "vision circuit" to feed the Dover transmitter was routed via London. Diagrams suggest there was also the option to feed the output from the Dover studio to Southampton, independently of the incoming ITV "network" feed. Such arrangements continued into the 1980s with TVS having studios at Maidstone as well as Southampton. Thornhill is around 5 miles from the Southampton Television Network Switching Centre, where the cables from BBC and ITV studios converged. For ITV the TV NSC also carried out circuit switching - the BBC arrangements were effectively static. All feeds to Rowridge ran via the TV NSC. For the BBC this allowed local programming to be substituted; ITV inserted advertisments as well as local programming - this included "play out" of Channel 4 advertising from 1982 to 1993. All feeds to the Rowridge transmitter therefore went back and forth between the TV NSC in central Southampton and Thornhill.
By around 1973 a link to Ryde had been added, providing additional capacity and reslience for telephony to the Isle of Wight. This appears to have been a replacement for temporary arrangements at Portsdown (also a Repeater Station on the Portsmouth to Southampton cable route). Early 1980s BT plans for migration to a digital network do not appear to have included the London to Southampton route (most television links remained analogue until the 1990s) but Thornhill featured in a proposed new link approaching from the west via Dean Hill, continuing via Butser Hill and the along the south coast. It is unclear how much of this link was ever completed - the sites at Dean Hill and Goodwood were subject to planning objections and existing non-BT sites were used on a limited basis.
