Britain's HF Radio Heritage: BT Radio Stations
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BT Radio Stations

I mentioned in the introduction to this series of articles about having driven past masts when I was a kid. There are two radio stations that contribute to this memory- Bodmin and Rugby: both BT Radio Stations. For those outside the UK, BT, formerly British Telecom, is the former Post Office Telephones department- up until privatisation a departnment of Her Majesty's Government. When radio communication first arrived on the scene, the government of the time 'gave it' to the Post Office to regulate and operate since it was seen as a parallel form of communication to ordinary mail.

The stations described within this section are undoubtedly the oldest HF transmitting and receiving stations in the UK; mostly they opened in around 1926 whereas overseas broadcasting on shortwave did not begin until 1932. The reason is that most of them were originally Marconi 'Beam' stations.

Marconi and the Imperial Beam Stations

Beam antennas at Dorchester Radio Station: Coutesy South Dorset Radio Society

Former MI5 officer Peter Wright wrote an interesting account of how the beam stations came to be, in his book Spycatcher. Wright's father was one of the people who were fortunate enough to work with Marconi in the early days.

By 1910, Marconi had set up stations that were providing regular and reliable communication with other countries, using the low frequency ('long wave') band, as was used in all of Marconi's early work. The British government, having seen this, wanted to set up a chain of long wave stations to provide communications with the Empire.

The Great War intervened and vitually no work was done on it until after the cessation of hostilities. By this time, Marconi had experimented enough with higher frrequencies to realise that great distances could be covered using lower powers, and that directional antennas could be used to concentrate the power in a particular direction. Furthermore, higher traffic speeds could be accomodated.

However the government was not convinced. Marconi therefore issued a challenge: He would build, free of charge, a link to anywhere in the world, provided the government would suspend work on the long wave chain until the 'beam system' and passed its trials, and provided that they would adopt the beam system should it be successful.

In response, the government gave a tough assignment: to provide a link from Grimsby to Sydney, Australia that would take less than 12 months to build, operate at 250 words-per-minute for 12 hours during the trial, and use less than 20kW of power. No doubt they thought this was impossible, and according to Peter Wright, even people close to Marconi were sceptical.

However according to Peter Wright it did work- and it worked well. It was ready in only 3 months and ran at 350wpm for 12 hour per day, 7 days a week.


G. Marconi
Known Beam Stations

The following is a list of known beam stations. As became common practice, transmitter stations were paired with a receiver station some tens of miles away.

Tetney: Tetney is located near Grimsby in Lincolnshire, and was paired with its receiver station at Winthorpe, just north of Skegness. Tetney was the 'pilot' station for the Beam system as described above.

It provided two services: to Sydenham near Melbourne in Australia, and to Dhond near Poona in India.. The Australian service used the callsign GBH and operated on a single wavelength of 25.096 metres (11954 kc/s). Of the two routes, the west-bound was longer (approx. 12,000 miles) than the east-bound (approx 9000 miles) and teh dircetion was switched to whichever had the longest part of its path in darkness- west in the morning, east in the evening.

The indian service operated on 35 metres (8.6 Mc/s) for the long path, and 19m (15.7 Mc/s)for the short path.

Dorchester: Paired with Somerton near Bridgwater in Somerset as the receiver station. Initially the station operated two services, to New York and to South America. These were supplemented by services to Japan and Egypt by 1928.

Ongar

Ongar beam station was located in Essex and was paired with Brentwood receiver station. The station operated two services, to Paris with callsign GLS and to Berne with callsign GLQ.

Equipment at Beam Stations

The typical beam station was equipped as follows. The transmitters were type SWB-1, this being short for Short Wave Beam, and generally pronounced 'swab' amongst engineers. They were specially designed for this service and used CAT2 or CAT3 power triodes in their final stages; these valves were cooled by paraffin (kerosene) but this was changed to water cooling at the start of WW2 to reduce the risk of fire in the event of the station being bombed..

The antenna was designed by C.S. Franklin of the Marconi company and was a curtain array of stacked dipoles (and presumably reflectors) for each service, suspended between 280 ft towers. Elements were cut for a number of different frequencies to permit day/night working were provided, and the elements could be switched to reverse the direction of the beam. At Tetney, the towers were spaced 650ft appart, and the total array was nearly a mile long. Twin feeders of copper tube were apparently used, which would have resulted in a very low loss feedline.

Last Modified 26/03/2010