Site Records

SiteName: Rugby Radio Station

OS Grid Ref: ('C' Building) SP553747

[Source: Malcolm Hancock]

by Malcolm Hancock (former station manager)
© British Telecommunications plc.
reproduced with permission from BT

To fully appreciate the history of Rugby Radio one must go back in time to the year 1910, for it was in this year that the newly formed Marconi Company approached the Colonial Office for licences for the construction of eighteen wireless stations throughout the British Empire.

While the idea proved of great interest to the Government, the general scheme was found to be unacceptable as it was felt that an undertaking of this magnitude should be in the hands of the Government and not a private concern.

After more than two years deliberation an agreement was concluded with the Marconi Company for the erection of six high power stations. The details of this agreement however, were severely criticised in Parliament and a Select Committee was appointed to report on it. The Select Committee in turn recommended the appointment of a committee of experts to examine the question from a technical point of view. This committee recommended certain modifications and a revised agreement was concluded in July 1913, ratified by the House of Commons and subsequently by the Dominion Governments concerned.

In December 1914, the Cabinet questioned how the Imperial stations would be affected by the war. As a result, they instructed the Postmaster General to terminate the contract with the Marconi Company as the Government had decided not to proceed with the Imperial Wireless Chain. At that date the erection of the masts at the English and Egyptian Stations had practically been completed and the mast material for the Indian station delivered.

At the end of 1919 the Committee were again sitting and after further wrangling with the
Dominions, who by then had definite thoughts of their own on how the scheme should operate an agreement for an Empire Chain of wireless stations was finally reached in 1922. Meanwhile a makeshift service using arc transmitters was in operation between Leafield in Oxfordshire and Abu Zabul in Egypt.

This was the position when the Coalition Government went out of Office but the situation was reconsidered in 1923 by the new Conservative Government, which decided to throw open Imperial Communications to private enterprise. At the same time they decided to erect a Government station equal in power to any in the world partly for strategic purpose and partly to prevent an absolute monopoly by the Marconi Company. This decision was announced by Mr. Bonar Law in the House of Commons on 5th March 1923 and with the purchase of about 920 acres of land at Hillmorton, (part being an old first world war airstrip) in the same year the Post Office embarked upon what was possibly its greatest single project up to that time, the building of Rugby Radio.

The site, approximately 340 feet above sea level and with a maximum variation in level throughout of 30 feet was chosen to accommodate sixteen masts each placed quarter of a mile apart. The aerial system was designed within the limit of structural possibilities, to give the best attainable radiation efficiency, the principal requirements being high effective height, high capacitance to earth and low earth resistance.

Rugby Radio main building
The aerial system consists of 820 feet masts (considerably higher than any masts previously constructed) spaced at quarter mile intervals, to form an irregular octagon with two extensions to the north, supporting cage aerials 12 feet in diameter. The aerial was constructed in two sections consisting of one large octagonal cage aerial two miles long supported on eight masts and another shorter cage aerial one and a quarter miles long supported on six masts, two of the masts being used in common with both sections of the aerial.

In all about 27 miles of copper cable were used in forming the aerial. The arrangement was such that the two sections could be connected together inside buildings to form one large aerial for extreme power. The masts, stayed in three directions at five levels are of braced steel construction and of uniform triangular section with 10 feet sides. The base is in the form of an inverted tripod, the apex of this being supported by a dome and hemispherical joint and insulated from earth by means of porcelain insulators and a block of Swedish granite. Each mast complete with stays weighs 200 tons and a sway of 10 feet at the top is possible. All the masts are fitted with electricity driven winches for
raising and lowering the aerial and also for operating an internal lift capable of carrying three persons.

When completed the aerial had a capacity of .045µF with an inductance of 358µH and a resistance of 0.4. The resistance to earth was 8M.. With all masts insulated the aerial had an effective height of 180 metres and an efficiency of about 29% at 16 kHz.

The normal working voltage of the aerial was 165,000 volts R.M.S. and the current at the base of the aerial about 750 amps. The earth systems consists of an open network containing about 120 miles of copper wire buried a few inches in the ground and occupying a space of 1600 feet wide under the length of the aerial.

The aerial system remained substantially unmodified over a period of 30 years, and only in 1956 was it necessary to renew the stays, a striking confirmation of soundness of judgment in the design.

The tuning coils of the transmitter were wound with Litzendraht cables consisting of 6,561 strands of No 36 SWG copper wire, each strand insulated with enamel and one covering of cotton or silk. The formers were hexagonal spiders of American white-wood, the external side being 7ft 9in in the largest former, and the turns were 6in apart. Five spiders of eight turns each formed the aerial coil, three spiders of four turns each the primary, and one spider of two turns the coupling coil

View of the aerial and earth systems

The transmitter itself was designed to operate at a frequency of 16kHz, the primary source being obtained from a valve maintained tuning fork vibrating at a frequency one-ninth of the radiated frequency. The output of the tuning fork stage was fed via a 50kW exciter stage to the final power amplifier units of which five were provided each containing eighteen 10 kW water cooled valves in parallel. The five amplifier units could be paralleled and allowed for one 500kW transmission with two spare units or two separate 300kW transmissions with one spare unit.

The High Tension Anode supply to the power units had to be capable of withstanding a short circuit with impunity and consisted of three sets of machines each consisting of a 3 phase 416V motor driving two d.c. generators. Each generator could develop 250kW at 3000V and all generators could be put in series thus giving 1500kW at 18000V.

The efficiency of the transmitter was about 72% excluding filament power or 65% including filament power. The transmitter was opened for traffic on 1st January 1926, under the callsign GBR, and having worldwide coverage was an unqualified success.

Aerial tuning coil

XXXXXXGBR VLF Telegraphy Transmitter 1926
Meanwhile, a second transmitter was being installed by Western Electric (later to become the ST&C Company in Britain) and experiments were carried out in radiotelephony between the United Kingdom and America. The outcome of these tests was the first two way telephone conversation across the Atlantic on 60kHz (GBT) and the inauguration of the Transatlantic Telephone Service in January 1927.

To continue the official history of Rugby Radio click here

[Source: Malcolm Hancock]

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