History
The London - Birmingham - Manchester route developed from the 1949 London - Birmingham 900 MHz Television Link A 2 GHz link was added over the southern section by the early 1960s but the main development was a few years after. Interim arrangements were put in place at Birmingham pending completion of the new radio tower. The route is accurately predicted on the 1956 "Backbone map" although Backbone itself followed revised plans. Three of the intermediate sites from the 1949 link were re-used, with new steel towers provided at Dunstable and Harrow Weald. Charwelton and the three new sites north of Birmingham received concrete towers of the "Chilterns" design. The London Terminal was at the Post Office Tower and at Birmigham a one-off design was used which incorporated elements of the "Chilterns" design but with equipment housed in the lower floor (as at London).The initial contract (23539) was awarded to GEC in 1962 for a "lower" 6 GHz system at a cost of £781,000. The contract required: "All main radio and bearer channel equipment to be completed, tested and ready for service by 1st July 1964" STC declined to quote "due to other commitments" and Marconi were unable to supply equipment for L6 GHz. This effectively allowed GEC to become the sole supplier for the London - Birmingham - Manchester route, but this was perhaps not realised at the time. Notes made during an audit of the Inland Microwave Network later in the 1960s show "ED confirm all in service 20/4/67" and a revised price of Â939,000 as of April 1966.
Two contracts were offered to GEC in 1965 on a non-competitive basis, for additional channels (300500) and addition of 4 GHz systems (300501) at cost of £90,000 and "to be advised" respectively, with completion dates of March 1968 and July 196 A further contract was offered to GEC and STC during 1966 for a 4 GHz system (300518) with offers of £585,000 and £680,000 received. The auditor comments, "from ED's recommendations" "As neither firm has yet developed a 4 Gc/s system of 1,800-channel capacity, it is necessary [...] to rely on our past experience[...] the GEC date of May, 1969 is considered to be realistic..." The detail of contract 300501 may have been recorded incorrectly but the effect of the decision for contract 300518 was to "lock out" STC from providing any 4 GHz equipment over the route.
By 1968 GEC had been contracted to provide systems in the "upper" 6 GHz band. Corresponence between the Post Office and GEC indicates delays with implementation and also with the 4 GHz system which was now being offered for service by early 1970. This implies the L6 GHz band was fully used by the late 1960s. Usage of 2 GHz is less clear: some TV links between London and Birmingham had used the band and "Backbone" traffic was moved from L6 GHZ to 2 GHz over the section between Pye Green and Sutton Common. There was discussion with GEC of the need for a new 2 GHz equipment design, potentially to be used on the London - Birmingham - Manchester route by the mid-1970s, suggesting all other bands would have been fully allocated by that stage.