The July 1977 network diagram for the TVNSC shows three vision circuits from London to Thornhill with two in the reverse direction. Incoming circuit V6 was connected directly to Rowridge, for BBC2. The other circuits went via the TVNSC where V4 was routed via to the BBC and V2 to the Southern studios. In contrast to the 1956 arrangement there was no permanent return route to London for the BBC - the Southampton studio output was connected to the Rowridge transmitter. Southern, however, had more elaborate arrangements. A "local" inbound circuit from their Chillerton Down transmitter was forwarded via Rowridge and the TVNSC to the studios - assumed to be for outside broadcast use. There were three outbound circuits from the studios, two were connected to London circuits V1 and V3, the third was routed via the link to Rowridge. As VHF 405-line television was still operational this circuit was extended to Chillerton Down. The independent circuits to London allowed for a dedicated link to the Dover transmitter (via a local studio) and an output to "network". In this version of the diagram there were potentially "spare" circuits between London and Thornhill which may have been used for telephony. Two "protection" circuits were available in each direction - the circuit numbers suggest one pair may have been part of a separate radio system.
The arrangements changed in November 1977 with V8 added from London to Thornhill. This was for BBC FM stereo distribution and routed directly to Rowridge, however despite the apparent availability of spare channels in the existing system the Link from Thornhill to Rowridge used a Pye M717 "TEMPY" (temporary) system. This was U6 GHz equipment. The ???
In the 1980s additional circuits were added for Channel 4 and TV-AM etc...