The Northern Radio Scheme was a series of connected links in north east Scotland and to the main Orkney and Shetland islands. Planning and construction took place over a number of years with the Annual Report to March 1957 advising that all equipment had been installed and overall tests of the links between Thrumster and Kirkwall (Wideford Hill) and to Lerwick (Shurton) were expected to be complete by May 1957 and that the link between Braewynner and Thrumster was also ready for final testing. The Kirkwall to Lerwick section was a VHF system with 48 channels – many years later the Shurton site was re-used for SHF purposes. The Braewynner <> Thrumster <> Wideford Hill links, however, operated at 4 GHz with 240 telephony channels. The equipment, designated RS10/2 was designed and manufactured by the Post Offce. The performance of these links was studied in some depth and whilst used to provide operational telephony circuits there seems to have been in parallel a plan to test a number of innovations.
The section from Braewynner to Thrumster was over a long sea path and diversity techniques were evaluated, with the simultaneous use of two frequencies and receiving antennas at different heights. Automatic switching was used to select the strongest signal from the two antennas and then that with the lowest noise content from the two frequencies. At both sites 325 ft guyed masts were used with two closely spaced dishes for transmission near the base and two dishes for reception near the top of the structure and widely spaced. The mast at Thrumster survives and is one of the longest-surviving antenna support structures in the PO/BT network (a similar mast at Golden Pot was operational from 1954 and survived in truncated form until 2016).
Between Thrumster and Wideford Hill the link used dishes mounted on relatively short towers – similar in style to those of the Manchester to Kirk o’Shotts television link. The tower and buildings at Wideford Hill appeared to be in place in 2016 although the site has expanded with new structures added.
These links were intended to be fully-integrated into the telephony trunk network – it was not expected that callers should be aware that SHF radio was involved. The multiplexing techniques for combining several calls into one radio link built upon those used for coaxial cable links.
Excluding the VHF link beyond Orkney, the 1957 Northern Radio Scheme used the sites at
Olrig Hill (intermediate repeater)
The route between Braewynner and Thrumster continued in operation until around 1978 – by this stage a new link running along the coast with shorter sea paths was brought into use. The site at Braewynner was subsequently cleared, the others remained in service with PO and BT and possibly still carry links to the Orkneys and Shetland Islands.