BT Tower - The Aerial Galleries
BT Tower - how it was in 2006
The Post Office Tower was designed to carry microwave aerials to beam telephone and television traffic across the country. Developments in high-capacity fibre optic cables have lead to the demise of such antiquated systems, and thus in December 2011 the redundant aerials were removed from the Tower.




Photo: BT Tower aerial galleries - how they used to look. Three of the original mauve-coloured horn aerials are visible © LSA 2006
| EXIT | The Aerial Galleries | Early Days | In Operation |  End of an Era |
Early Days
 
In the beginning, just four microwave routes to and from the Tower were planned, but the aerial galleries had plenty of space to accommodate additional aerials. Models of the Tower, (such as the one below) demonstrated possible combinations of large and small, horn and dish configurations.

Model of the aerial galleries.
"The most striking feature of the galleries is the large horn-reflector-type aerials, two of which are used for each of the four principal routes from the Tower." - POEEJ October 1965.







The model opposite shows the possible configurations of horn and dish aerials which could have been deployed on the Tower.




Photo: Model of the Tower aerial galleries © LSA June 2008. Exhibit held by Science Museum, London.
In Operation  
The original horn aerial configuration
Originally, four pairs of horn aerials carried microwave traffic to four compass points:



"...four main microwave radio paths - from London towards Birmingham, Coventry and the North; toward Southampton, Bristol and the West and also for the satellite communication ground station at Goonhilly Downs; toward Dover, Folkestone and the Continent; and toward Norwich and the North-East of England."







Reproduced in the Post Office Telecommunications Journal, Winter 1965: "This remarkable picture shows four of the eight horn-paraboloid reflector aerials which are an outstanding feature of the Tower." Picture by Brian Seed. Copyright the Illustrated London News.
   
Retrospective (2020)

The evidence available, suggests that the original plan for eight horn aerials was never fully realised, and a total of only seven were ever fitted. This ties-in with the article below, whereby five were removed in 2011. It is surmised that two horn aerials had been removed by 1986, as digital dish routes were added.

End of an Era (2011)

It was 'back to basics' at the Tower in early December 2011 when the 5 remaining original horn aerials were finally removed for health and safety reasons. And 24 'modern' circular dish aerials, which were in service between 1986 to 2006, were also dismantled, leaving the galleries devoid of core aerials.

The circular and dish microwave aerials of the Tower were superseded by fibre optic cable routings, circa 2006. Weathering by wind and rain had caused corrosion and led to loosening of the covers, junction boxes and brackets.

Although the aerials and associated equipment didn't form part of the 2003 Grade II Listing, their removal did alter the overall appearance of the Tower and was an initial concern. However, it was stated that the changing character of the building is true to the very nature of the Tower in that it evolves over the years, as communication technology changes. A range of small aerials, for outside broadcast uses, will remain in situ and continue to be operational.

The original horn aerials were thought to have been taken out of service between 1981 and 1986. Each of these pyramidal horns weighed 1 ton and were 27ft. high by 14ft. wide. The radiating aperture was enclosed by a Hypalon-coated terylene sheet, which allowed the aerial and waveguide to be pressurised, by dry air, to keep the cover taut and to prevent the ingress of moisture. The air compressors were left operating to preserve the condition of the obsolete horn aerials, but a point was reached when it was no longer possible to maintain this equipment and thus the covers became loose and the weather began to erode the structures.

It is worth noting that DuPont ceased producing Hypalon® and closed the plant in April 2010.
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