Tower Trunk Units
Tower Trunk Units
In the early Sixties, the General Post Office, as it then was, began building a tower that would be able to carry all of the microwave traffic into and out of London. Thus by 1965, the newly completed structure of the Post Office Radio Tower in Howland Street was the tallest building in Britain.
| EXIT | Tower Trunk Units | STD in London | Trunk Test | Datel Test Centre |
In 1944, Howland Street was home only to Museum telephone exchange, and later a small microwave radio mast, situated on top of the building . The new Tower complex was to comprise, the old Museum telephone exchange, the Post Office Tower and television switching, as well as new STD trunk units... 
At the Post Office Tower

The main feature of the Tower was the aerial galleries, initially providing four microwave radio links from London towards:

  • Birmingham, Coventry and the north.
  • Southampton, Bristol and the west (including Goonhilly Satellite Station).
  • Dover, Folkestone and the Continent.
  • Norwich and the north-east.
The microwave systems were designed to carry both Telephony and Television circuits, including the new BBC2 service.

Also being developed at this time was the telephone trunk switching network...

Subscriber Trunk Dialling (STD) in London

A total of four Outgoing RT units were planned:
 
  • Citadel in Faraday Building.
  • Fortress in Fore Street.
  • Tower in Howland Street.
  • Bastion in Temple Bar.
Tower Trunk Units

The switching units for the Tower were housed in a four storey building adjoining the main structure with a staff of 270 engineers.

Tower Non-Director O/G ( July 1965)

For traffic originated in London, the Tower ND Unit was made up of:

  • 3000 incoming relay sets.
  • 11 magnetic drum type Register-Translators.
  • 5000 selectors.
  • 1500  O/G trunk signalling relay sets.
Graham Hall adds...

"The Tower GSC (Group Switching Centre) unit is quite clearly understated. The outgoing unit may have originally been installed with 11 RT4 drums, but when I maintained them around 1970 - 80, the installation was 22. This is of course not really important, but the people who worked in large teams on these units should be remembered. The great characters that seem to have been lost from today's working environment? People like Vince Coppola (AEE), Dennis Judge (TOA) and Alan Poole (TOA)."


Mercury Non-Director I/C ( November 1965)

For trunk traffic coming into London, Mercury ND was made up of:
 
  • 4000 I/C trunk signalling relay sets.
  • 11000 selectors .
  • electronic ferrite-core type Register-Translators.
Museum Main Tandem (April 1966)

A junction tandem exchange was necessary to switch calls between various local Director exchanges within London:

  • 1200 selectors.
  • O/G access via Mercury ND.
London Television Switching Centre (on 3rd floor)

A very important service was the switching and distribution of television programmes, adverts pictures and sounds for the BBC and ITA as well as links for radio broadcasts. In the 1990s this included, Channel 4, ITV2, Satellite and Digital TV. A large number of dedicated circuits are rented by the television companies while others are brought on-line as required, e.g. for seasonal sporting events such as Wimbledon Fortnight.

Trunk Test

  • TMCC (Trunk Maintenance Control Centre) controlling 5500 O/G Trunks, 16200 O/G Junctions from 27 test positions.
  • PCMCC (Private Circuit Maintenance Control Centre) controlling 1400 Private Circuits with 3000 spurs (Speech & data) from 9 test positions.
  • The Datel Test Centre.
The Datel Test Centre
Datel Test Centre
The London Datel Test Centre at the Tower.

Colin Atkinson, working at the time for London East Datacomms, recalls a visit in 1976 to check out the test equipment...
   
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