History

A route between Birmingham and Bristol appears on a 1959 network diagram as "planned (sites not determined)", running via Wotton-under-Edge. These plans were not progressed until the late 1960s: a document headed "1967/68 PROGRAM WORKS" includes "The provision of two two-way operational channels each of 1800 circuit capacity, and one two-way protection channel between Bristol (Purdown) and Birmingham (Tower)". The document shows total estimated expenditure of £280,000 - with £200,000 in the financial year 1969-70

Two new sites were required at Bredon Hill and Cinderford. The option of routing via Wotton-under-Edge was abandonned, possibly since this would have limited the capacity of the Birmingham and London routes due to the shared section. The route ran directly between Cinderford and Purdown and opened once the new concrete tower at Purdown was available. The two intermediate sites were originally provided with cable stayed masts, limiting the capacity of the route. A 1970s document on trunk network development mentions planning restrictions as a factor impacting the expansion of traffic over the Birmingham - Bristol route, however capacity was increased during the 1980s.

As indicated above, the route was initially established for telephony: television circuits between Bristol and Birmingham were routed via London, largely as a consequence of the way the BBC and ITV distribution networks developed. By the 1980s, however, the IBA had a single vision circuit in the Birmingham to Bristol direction - this could be switched at Bristol towards Cardiff, Plymouth or London; there does not appear to have been a local destination in the Bristol area. The BBC also rented a single vision circuit from Birmingham to Cardiff which ran via Purdown - this was used to for VHF radio distribution rather than television.

Traffic over the Birmingham - Bristol route increased from 1978 onwards with the opening of a satellite "earth station" at Madley. Circuits ran via cable to a new SHF station at Coldwell which was in turn linked to Cinderford. At the time it was the general practice for all "external" traffic to be routed via London - irrespective of the UK end-point for the call. Initially circuits ran south via Purdown and onto the Bristol - London route, however this was heavily used for telephony and television and already carried circuits from Goonhilly. Subsequently traffic from Coldwell was taken north at Cinderford towards Birmingham where additional capacity to London was available via cable routes and other SHF links.

In 198? the masts at Bredon Hill and Cinderford were replaced by towers of the "Type 8A" pattern. This allowed additional bands to be used. Digital systems were introduced initially at 11 GHz. Existing links at 4 GHz and 6 GHz bands were then migrated, with full use of all bands by the 1990s. The Coldwell Spur closed by 2004 - an alternative route from Madley to Birmingham was built in the 1980s.