British Telecom microwave network
Encyclopedia
The British Telecom microwave network was a network of point-to-point microwave radio links in the United Kingdom, operated at first by the General Post Office, and subsequently by its successor BT plc. From the late 1950s to the 1980s it provided a large part of BT's trunk communications capacity, and carried telephone, television and radar signals and digital data, both civil and military. Its use of line-of-sight microwave transmission was particularly important during the Cold War
for its resilience against nuclear attack. It was rendered obsolete, at least for normal civilian purposes, by the installation of a national fibre optic communication network with considerably higher reliability and vastly greater capacity.
BT remains one of the largest owners of transmission and microwave towers in the UK. The most famous of these is the BT Tower
in London
, which was the tallest building in the UK from its construction in the 1960s until the early 1980s, and a major node in the BT microwave network.
BBC television.
for an experiment in the relaying of television signals to Birmingham. In this case, the signals from Alexandra Palace were to be received at Dunstable and transmitted over a radio link to Sharmans Hill, Charwelton, some 40 miles distant towards Birmingham; thus carrying the signal two-thirds of the way from London to Birmingham. World War II
intervened and this early experiment had to be abandoned.
with a deviation of 6 MHz per volt. Each relay station consisted essentially of back-to-back rhombic antenna
s on opposite sides of a hilltop, connected via an amplifier. The frequency was not changed. The system was first tested on March 24, 1949. The stations were located at:
. The contract for this was placed with GEC in mid-1947. The stations were located at:
. This was the first permanent GPO system to use the 4 GHz band. The chain was routed near the east coast in order to be close to Leeds, Newcastle and Edinburgh. The stations were located at:
The term 'backbone
' is often applied to the core of a communications network, i.e. the part that provides high-capacity links over long distances between major nodes. In the early 1950s, the term was used by the General Post Office (BT's predecessor) to describe a chain of microwave links designed to provide resilient communications in the event of nuclear war
. It was originally designed as a chain of stations between south-east England and Scotland.
The exact location of the Backbone sites changed as the project was developed, but in July 1956 there were 14 planned sites at (from south to north):
Two additional 'Backbone spur' sites were planned for Shrewsbury and Grantham, which connected to the main Backbone spine at Pye Green and Coalville respectively.
Many of the towers were designed with particular types of antenna in mind. Many towers were designed to carry horn antennas but no longer do so, and look rather odd as a result.
Cold War
The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...
for its resilience against nuclear attack. It was rendered obsolete, at least for normal civilian purposes, by the installation of a national fibre optic communication network with considerably higher reliability and vastly greater capacity.
BT remains one of the largest owners of transmission and microwave towers in the UK. The most famous of these is the BT Tower
BT Tower
The BT Tower is a tall cylindrical building in London, United Kingdom, located at 60 Cleveland Street, Fitzrovia W1T 4JZ, London Borough of Camden. It has been previously known as the Post Office Tower, the London Telecom Tower and the British Telecom Tower. The main structure is tall, with a...
in London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...
, which was the tallest building in the UK from its construction in the 1960s until the early 1980s, and a major node in the BT microwave network.
Television links
The earliest operational GPO microwave links were provided for 405-line405-line
The 405-line monochrome analogue television broadcasting system was the first fully electronic television system to be used in regular broadcasting....
BBC television.
London to Birmingham pre-war
In 1939 the Post Office placed a contract with EMIEMI
The EMI Group, also known as EMI Music or simply EMI, is a multinational music company headquartered in London, United Kingdom. It is the fourth-largest business group and family of record labels in the recording industry and one of the "big four" record companies. EMI Group also has a major...
for an experiment in the relaying of television signals to Birmingham. In this case, the signals from Alexandra Palace were to be received at Dunstable and transmitted over a radio link to Sharmans Hill, Charwelton, some 40 miles distant towards Birmingham; thus carrying the signal two-thirds of the way from London to Birmingham. World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
intervened and this early experiment had to be abandoned.
London to Castleton 195 MHz
The GPO built in an experimental chain of radio relay stations for television, which used the relatively low VHF frequency of 195 MHz and frequency modulationFrequency modulation
In telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
with a deviation of 6 MHz per volt. Each relay station consisted essentially of back-to-back rhombic antenna
Rhombic antenna
A rhombic antenna is a broadband directional antenna co-invented by Edmond Bruce and Harald Friis, mostly commonly used in HF ranges.- Technical Detail :...
s on opposite sides of a hilltop, connected via an amplifier. The frequency was not changed. The system was first tested on March 24, 1949. The stations were located at:
- Rowley Lodge, near Barnet, Hertfordshire
- Green Hailey, Buckinghamshire
- Widley, Hampshire
- Hook, Hampshire
- Wotton-under-Edge, Gloucestershire
- Post Office Radio Laboratory at Castleton, Monmouthshire
London to Castleton 4 GHz
The GPO built an experimental 4 GHz system. This was used operationally to feed TV pictures to the Wenvoe transmitter during the latter's first four months on air in late 1952, until a coaxial feed became available. Some of this equipment from this link was recovered, refurbished, modified and used to provide a permanent link from London to Rowridge in 1954.London to Birmingham 900 MHz
A chain of stations was built between telephone exchanges in London and Birmingham to connect the Sutton Coldfield transmitting station to Alexandra PalaceAlexandra Palace
Alexandra Palace is a building in North London, England. It stands in Alexandra Park, in an area between Hornsey, Muswell Hill and Wood Green...
. The contract for this was placed with GEC in mid-1947. The stations were located at:
- London Museum exchange
- Harrow Weald, Middlesex
- Zouches FarmZouches FarmZouches Farm is a microwave radio link site located near the top of Blows Downs at Zouches Farm, Caddington, Bedfordshire, England . It was part of the London to Birmingham chain designed in the 1940s, and is now owned and maintained by BT Group....
, Hertfordshire - CharweltonCharwelton BT TowerCharwelton BT Tower is a telecommunication tower built of reinforced concrete at Charwelton near Byfield, Northamptonshire, England. It is tall and one of the few British towers built of reinforced concrete. It is a landmark for miles around.-See also:...
, Northamptonshire - Turner's Hill, Staffordshire
- Birmingham Telephone House, Warwickshire
Manchester to Kirk o'Shotts
The GPO placed a contract in July 1950 for a chain of microwave links to feed BBC television from Manchester to the Kirk o'Shotts transmitting stationKirk o'Shotts transmitting station
The Kirk o'Shotts transmitting station is a broadcasting and telecommunications site at The Hirst which lies just outside the village of Salsburgh which is near the town of Shotts in North Lanarkshire central Scotland...
. This was the first permanent GPO system to use the 4 GHz band. The chain was routed near the east coast in order to be close to Leeds, Newcastle and Edinburgh. The stations were located at:
- Manchester Telephone House
- Windy HillWindy Hill (Pennines)Windy Hill is a hill in Greater Manchester, and a part of the South Pennines, in northern England. It is located between the A672 road and Junction 22 of the M62 Motorway, just within the Metropolitan Borough of Rochdale; West Yorkshire is immediately to the east. A radio transmitter is located at...
, Lancashire - TinshillTinshillTinshill is a district of Leeds, 4 miles north of Leeds city centre, West Yorkshire, England. It is situated between Horsforth and Cookridge. When the estate was planned in the 1940s it was originally known as the 'Cookridge Tower Estate'. The estate predated surrounding estates such as...
, Yorkshire - Arncliffe Wood, Yorkshire
- Pontop Pike, County Durham
- Corby's Crags, Northumberland
- Blackcastle Hill, East Lothian
- Blackford HillBlackford HillBlackford Hill is a hill in the south of the Scottish capital city of Edinburgh, in the area of Blackford, near Morningside, The Grange, and the Braid Hills....
, Midlothian - Kirk o'ShottsKirk o'Shotts transmitting stationThe Kirk o'Shotts transmitting station is a broadcasting and telecommunications site at The Hirst which lies just outside the village of Salsburgh which is near the town of Shotts in North Lanarkshire central Scotland...
, Lanarkshire
Backbone
Backbone network
A backbone network or network backbone is a part of computer network infrastructure that interconnects various pieces of network, providing a path for the exchange of information between different LANs or subnetworks. A backbone can tie together diverse networks in the same building, in different...
' is often applied to the core of a communications network, i.e. the part that provides high-capacity links over long distances between major nodes. In the early 1950s, the term was used by the General Post Office (BT's predecessor) to describe a chain of microwave links designed to provide resilient communications in the event of nuclear war
Nuclear warfare
Nuclear warfare, or atomic warfare, is a military conflict or political strategy in which nuclear weaponry is detonated on an opponent. Compared to conventional warfare, nuclear warfare can be vastly more destructive in range and extent of damage...
. It was originally designed as a chain of stations between south-east England and Scotland.
The exact location of the Backbone sites changed as the project was developed, but in July 1956 there were 14 planned sites at (from south to north):
- Tring, Hertfordshire
- Charwelton, Northamptonshire
- Coalville, Leicestershire
- Pye Green BT TowerPye Green BT TowerPye Green BT Tower is a 388 ft tall, telecommunication tower built of reinforced concrete at Pye Green, Staffordshire, England . Standing in Cannock Chase it is one of the few telecommunication towers in the United Kingdom built of reinforced concrete...
, Staffordshire - Sutton CommonSutton Common BT TowerSutton Common BT Tower is a radio tower built of reinforced concrete at Macclesfield, Cheshire, England. It is one of the few communication towers in the United Kingdom built of reinforced concrete...
, Cheshire - Saddleworth, Yorkshire (Saddleworth is now in Greater ManchesterGreater ManchesterGreater Manchester is a metropolitan county in North West England, with a population of 2.6 million. It encompasses one of the largest metropolitan areas in the United Kingdom and comprises ten metropolitan boroughs: Bolton, Bury, Oldham, Rochdale, Stockport, Tameside, Trafford, Wigan, and the...
) - Hunters Stones, near Skipton, Yorkshire
- Azerley, Yorkshire
- Richmond, Yorkshire
- MuggleswickMuggleswickMuggleswick is a village and civil parish in County Durham, England. It is situated a few miles to the west of Consett.The village has a number of farms and domestic dwellings as well as the Church of England church, generally accepted as dedicated to All Saints, and village hall . Amenities other...
, Co. Durham - Cold Fell, Cumberland
- Lockerbie, Dumfriesshire
- Green Lowther, Dumfriesshire
- Kirk o'ShottsKirk o'Shotts transmitting stationThe Kirk o'Shotts transmitting station is a broadcasting and telecommunications site at The Hirst which lies just outside the village of Salsburgh which is near the town of Shotts in North Lanarkshire central Scotland...
, Lanarkshire (GPO site near BBC site)
Two additional 'Backbone spur' sites were planned for Shrewsbury and Grantham, which connected to the main Backbone spine at Pye Green and Coalville respectively.
Radio standby to line
The 1956 GPO paper referred to under 'Backbone' above also described a series of links called 'radio standby to line'. These were spur links between the GPO Backbone sites and defence 'customer' sites. They were designed to carry between 25 and 150 'private wire' (a.k.a. leased line) circuits each, by radio. The paper contains a list of sites and a network map, showing the following radio standby to line links:- Kirk o'Shotts to Gailes GCI radar station near Ayr
- MuggleswickMuggleswickMuggleswick is a village and civil parish in County Durham, England. It is situated a few miles to the west of Consett.The village has a number of farms and domestic dwellings as well as the Church of England church, generally accepted as dedicated to All Saints, and village hall . Amenities other...
to Boulmer GCI station, ROC and regional communications, Seaton Snook GCI station - Hunters Stones to Forest Moor Admiralty radio receiving station, Shipton RAF 'Sector Operations Centre' (SOC), Preston SOC, Regional Commissioner's HQ and Admiralty radio transmitting station
- Grantham to RAF bomber bases and US Air Force bases
- Norwich to RAF SOC (Bawburgh), US Air Force bases, GCI stations, naval headquarters, Continental communications
- Kelvedon HatchKelvedon HatchKelvedon Hatch is a village and civil parish in the Borough of Brentwood in south Essex, England. It is situated just north of Pilgrims Hatch, approximately to the north of Brentwood and is surrounded by Metropolitan Green Belt. The village today is no longer a rural backwater with a large...
to RAF SOC, RAF bomber stations, RAF radar stations - West Malling to naval headquarters at Chatham and Dover, RAF radar and Fighter Command headquarters, Continental communications
- Upavon to Army establishments on Salisbury Plain
- Sopley and Portsmouth to naval headquarters at Portsmouth and naval radio stations at Horsea and Flowerdown
- Box to Admiralty establishment at Bath, RAF SOC and Signals centre, Army signals centres at Cheltenham and Droitwich and Army radio stations, Foreign Office GCHQ and radio stations, important radio stations and miscellaneous radar stations in south-west England, South Wales and the Border Counties.
Antennas and towers
Various types of antenna have been used in the network's history. At first, prime-focus parabolic reflectors were used. In about 1960, dual-band horn antennas started to be used widely, and a few of these survive to the present day. They began to go out of fashion at the end of the 1960s, when types of parabolic antenna with an improved performance became available.Many of the towers were designed with particular types of antenna in mind. Many towers were designed to carry horn antennas but no longer do so, and look rather odd as a result.
Further reading
- Campbell, D.Duncan Campbell (investigative journalist)Duncan Campbell is a British freelance investigative journalist, author and television producer who, since 1975, has specialised in the subjects of intelligence and security services, defence, policing, civil liberties and, latterly, computer forensics. He was a staff writer at the New Statesman...
, 1983. War Plan UK, p243, p245. Paladin edition. ISBN 0-586-08479-7. - Laurie, P., 1983. Beneath the City Streets, p.243. Granada edition. ISBN 0-586-05055-8.
- The National Archives (UK)The National Archives (UK)The National Archives is a UK government department and an executive agency of the Secretary of State for Justice. It is "the UK government's official archive, containing 1,000 years of history"...
, 1956-1962. Proposed relay station sites for the General Post Office ("The Backbone Scheme"). File No. COU1/38. - Fox, S., and Lamont, R., 2003. The Towers of Backbone.