History
Blackcastle Hill seems to have been a constant in a changing network. Initially linking between Corbys Craggs and Blackford Hill as part of the 1951 Manchester to Kirk o'Shotts television link the original tower here was of the same style as elsewhere but a 200 ft version was required to clear the terrain to the next stations. An unexpected problem, due to the angle between the routes, was reflection from the "back" of the dishes - this was overcome by the addition of mesh screening.
The TV route was planned with the option of a site at Wooler but this was found not to be required - however it was introduced again around 1967 as part of a link from Dundonald to Boulmer for the Linesman radar system. The Linesman link also saw the use of Craiglockhart as a replacement for Blackford Hill. The original television route was taken out of service by the mid-1960s as later circuits from Manchester to Kirk o'Shotts ran via Carlisle.
The site was used from around 1963 as part of the northern section of "Backbone". Archive photos suggest for a time this involved a single "hop" to Craigowl - this would have involved a relatively long path and it seems the route was later routed via East Lomond. The current tower appears to have been fully operational by 1965, with horn antennas supported from steelwork added to the basic structure. The orientation of the tower has required further additions to allow dishes to be aligned facing Craiglockhart and Wooler. Although the dishes have been removed the steelwork remains as evidence.
A stress analysis was carried out in 1971 prior to modifications to the tower. The archived documents show a total of eight 12 ft dishes facing Wooler, seven towards Craiglockhart and two 8 ft dishes at low level facing East Lomond. This is assumed to have been the forecast maximum load once all bands were fully utilised. It is likely the two smaller dishes reflect the need for "diversity" to overcome tidal fading on what would otherwise seem to be an "easy" path to East Lomond. There is no mention of Craigowl (or Corbys Craggs) on the diagram. Photos of East Lomond from around 2006 confirm the Backbone link across the Forth Estuary was withdrawn before general closure of the network, leaving Blackcastle Hill as the penultimate station on a telephony route serving Edinburgh. The site remains in use by mobile phone networks and other users and work was recently undertaken by LARS Communications to strengthen the tower.
Blackcastle Hill features in the opening scene of the 1965 GPO film "Microwave Aerials and Towers" - with the "new" tower alongside the one for the 1951 televison link. Later scenes show the foundations and tower under construction. (The closing minutes show a horn antenna being delivered to site however the final scene shows installation on a different, much shorter tower!)
