History

Note: the map shows the modified route via Wharrels Hill. See London - Belfast (TV) for the original configuration.

Carlisle - Belfast was a relatively ambitious scheme combining television and telephony links. This involved a relatively long sea path and integration of vision and telephony circuits into the same system, building on experience with the Northern Radio Scheme and development work for the cross-channel TV/telephony link.

Contract 21841 was awarded to STC in June 1958, for a 4 GHz system. The initial requirement was for "two channels in the direction Carlisle - Belfast by April 1959" and is understood to have been provided as a vision circuit for ITA, plus "protection channel". The cost was agreed as £118,046, the bids of £122,656 from Marconi and of just £49,868 from GEC(noted as "incomplete") were rejected. Notes show the "Ready for Service" date was extended to September 1959 due to "Delay in providing buildings" and the actual completion date is given as May 1961. UTV commenced broadcasting on 31 October 1959 which suggests the system was operational on an interim basis even if not techincally complete. By May 1966 the total cost had risen to £129,615 but the work was "taken over" on 1 August 1964, ending the contractor's initial maintenance period.

The Carlisle terminal was established at the Harraby repeater station - this was on the cable routes between Manchester and Scotland and an incoming ITA "network" feed was available. Three intermediate sites were required, each received a permanent buiding based on contemporary exchange designs, together with a "pylon" style tower. The Belfast terminal was at the existing Ballygomartin radio station with a cable link to Telephone House. In due course a Television Network Switching Centres (TVNSC) was established at both ends of the link.

Contract 23553 was awarded in January 1964 for "additional channels", with further contracts 300509 and 300514 in 1966. The later contracts were required for 1 August 1967 and 1 January 1968 - these may relate to vision circuits to 625-line colour standards. As was the practice at the time, contracts for additional channels were awarded to the original contractor (STC).

The route between Carlisle and Kirk o'Shotts also ran via the intermediate site at Riddingshill - this operated initially in the L6 GHz band. The shared section between Carlisle and Riddingshill limited the capacity of both routes and in 196? the Belfast route was diverted via a new site at Wharell's Hill, removing this bottleneck.

In the 1980s an 11 GHz system was installed between Carlisle and Belfast. At the time of closure this 5+1 system carried three telephony systems together with a link for Channel 4 television. A U6 GHz 7+1 system (supplied by STC) carried a single telephony system along with six vision circuits. It appears the 4 GHz system had been withdrawn from service by this stage.

A network diagram for the Belfast TVNSC dated 1984 shows two outgoing vision circuits from Belfast (one each for BBC and ITV).