History
The Northern Radio Scheme comprised two microwave links together with VHF radio systems. It was significant as the first SHF telephony link integrated with the trunk network - other SHF links from this period were to meet television requirements. In some ways a prototype system, the link between Braewynner and Thrumster remained in operation until 1978 (replaced by a new route running along the coast, see Offshore Oil & Gas).The original installation was documented in some detail (see links alongside) and used equipment of Post Office design (RS 10/2) between Braewynner and Thrumster with STC RL4B equipment (RS 10/3) between Thrumster and Wideford Hill. The southern section, over a 55 mile sea path was described at the time as "...unusually long for a single-hop link in a 4,000 Mc/s system." [POEEJ Volume 40, Part 2, page 106]. The strategy to overcome potential problems with tidal fading was to use a "twin path" system - the link transmitted on two frequencies simultaneously - and "height diversity" with antennas at different levels. At the receiving end of the link the best signal was selected automatically, with fast switching between frequencies and antennas.
The frequencies used do not fit within the later "band plan" for 4 GHz and the capacity of the system (240 circuits, also known as four "supergroups") was somewhat lower than subsequent telephony links. It is not known whether the equipment was upgraded or continued in use until the new route was available.