History

This was not a core route in the Post Office/BT network but used for televison distribution. The pre-history began with the award of a contract to Southern Television in 1958. The region covered from Dorset to Kent, requiring a transmitter at Dover. The company established studios in Southampton with a transmitter at Chillerton Down on the Isle of Wight and the Post Office provided a link from London. When the Dover transmitter entered service in 1960 this required a "vision circuit" from Southampton - was provided as a return channel on the Isle of Wight system, connected to one "tube" in the London - Dover/St Margaret's Bay trunk cable.

Southern also established a studio at Dover in 1961. To allow this to feed the Chillerton Down transmitter (or elsewhere) required a further link towards London, also provided on the trunk cable. These arrangements were satisfactory for VHF 405-line television - it was not unusual for trunk cable to be used for vision circuits.

The introduction of 625-line colour televison in the late 1960s required higher bandwidth vision circuits - this was more difficult to provide over "long" cable sections and was a factor in the expansion of the microwave network. The needs of Southern Television were to be met through the replacement London - Southampton system and the planned SHF link between London and Tolsford Hill, with a short cable connection for Dover. Various factors delayed the completion of both sections however the Dover UHF transmitter entered service for ITV in December 1969.

The Dover link ran from the London Television Network Switching Centre (TVNSC) via newly-completed sites at Fairseat and Flimwell to the existing SHF site at Tolsford Hill where a TVNSC had been established to control cross-channel EBU ("Eurovision") links originally installed in 1959 - these also used cable connections to and from London. A network diagram from mid-1977 shows the vision circuits for Southern were extended from Tolsford Hill over a coaxial cable to Dover, via Folkestone and three other repeater stations. From Dover (exchange) cables ran to the transmitter and studio with switching allowing the transmitter to be fed directly from the incoming vision circuit. The studio output could be switched to the local transmitter but was also sent to London (normally routed onwards to Southampton). It was also possible for the incoming and outgoing circuits at the Dover studio to be looped - this may have been the normal setting since the studio operated part-time but this would have allowed an end-to-end check of the circuits. The switching options allowed the studio output to be sent to Southampton whilst the transmitter carried the main programme. It's likely a similar configuration had available in 1961. These arrangements remained in place until the Dover studio closed in 1983.

A 1984 revision to the Tolsford Hill TVNSC network diagram shows there were then two inbound vision circuits: one from London, the other from Maidstone. This reflects the addition of a link for Channel 4 (on-air November 1982) and the ITV franchise transfer to TVS which estabished studios at Maidstone (operational mid-1983). The cable link to the transmitter was reconfigured since there was no longer a need to go via Dover exchange. The return link towards London remained, unconnected, and is labelled as terminating at Fairseat. The 1984 arrangement was to be relatively short-lived: Channel 4 moved to a new distribution network on 1 January 1993 and the ITV franchise transferred to Meridian on he same date. Meridian appears to have been an early adopter of digital/fibre links. The Eurovision circuits appear to have been unchanged as of 1984: one link in each direction but with access to the protection circuits on the other systems. This allowed additional capacity for major events.

The BBC was permitted to make its own arrangements for the Dover transmitter: for many years this involved off-air reception from London (Crystal Palace) followed by microwave links via other BBC sites.

During the TVS era a remote-controlled TVNSC was added at Fairseat (operated from Tolsford Hill). This was presumably intended to simplify switching since the company operated three studios in Kent at various times: Dover, Gillingham and Maidstone. Before mid-1983 it would have been necessary to route Dover or Gillingham to London (for Southampton). Gillingham was retained once Maidstone had opened and most likely the two were connected "directly". Maidstone could be connected "permanently" to both London and the Dover transmitter - however the arrangements for TV-am (1983-1992) required BT to provide direct links from London to the transmitters, bypassing the regional ITV studios. It's possible the remote switching at Fairseat was retained to bypass Maidstone during TV-am hours.

A network diagram for the London TVNSC, dated November 1984, shows several vision circuits to and from Maidstone "RTSC" - possibly Remote Television Switching Centre - suggesting there were three inbound circuits and two outbound. Both outbound circuits appear to have been cross-connected to Southampton, as was one inbound circuit. The other two inbound circuits were connected to the main switching matrix. No direct route to the Dover transmitter is shown at the London end - it appears all circuits went via Maidstone and it seems likely the TV-am switching was ultimately carried out there. The TVS studios were within two miles of the Maidstone exchange.