Site Records

SiteName: Rugby Radio Station

Rugby
Warwickshire
OS Grid Ref: ('C' Building) SP553747

Long wave transatlantic telephony transmitter 1927

The tuning coils were similar to those in use on GBR and part of the original aerial system was adapted for the transmission which could also be radiated on 68 kHz (GBY). A fourth d.c. generator was installed to furnish the EHT supply to this transmitter and was of similar design to the previous three except that it had an output of 12kV using two 6kV generators in series. The main capacitors for both transmitters were housed on the first floor and consisted of series/parallel combination using mica insulation and suspended in oil filled steel tanks.

A third transmitter of 50kW output was also built and utilised for telegraph broadcasts to Europe, on a frequency of 78kHz. Again water cooled valves were used and the transmitter was frequency controlled by means of a tuning fork vibrating at a seventeenth of the radiated frequency. Use was made of the two masts nearest the buildings to support a "T" type cage aerial similar to those in use on the two previous transmitters.

The use of so many water cooled valves necessitated the building of two reservoirs each with a capacity of about quarter of a million gallons of water, and a heat exchange system to cool the distilled water flowing through the valves.

The original receiving station was at Wroughton in Wiltshire, and employed a Beverage aerial, five miles long. Later, in order to reduce noise on the circuit a receiving station was installed much further north, at Cupar in Fifeshire. Again a Beverage aerial was used but it was subsequently replaced by loops extending over an area of several square miles.

At such wavelengths construction of highly directive aerial arrays became practicable and radiated power could be concentrated in the direction of the receiving station resulting in a considerable reduction in the cost of establishing a radio telephone circuit.

After the establishment of short wave radiotelephone communication from Rugby Radio a second building ('A' Building) was set up half a mile from the site of the original to cater for the installation of further short wave transmitters.

View of 'A' building c.1932

Short wave transmitters in 'A' building in 1934

Rapid expansion of short wave radiotelephone services followed equipment of the 'A' building in 1929 and plans for building low frequency transmitters were dropped.
By then the transmitters were frequency controlled by means of a temperature stabilised quartz crystal excited oscillator, followed by frequency multipliers and amplifiers up to a power of about 60kW and modulated by speech in the low power stages and this remained the basic design over a number of years.

The filament, grid bias and intermediate HT supplies were obtained from d.c. generators driven by a.c. synchronous Motors while the final HT voltage was from thermionic valve rectifiers. Although, at this time, the merits of single sideband operation had been well proven it was not possible to control the frequencies of HF oscillators with the necessary precision and double sideband was therefore used.

The aerials in general were various patterns of arrays of half wave elements and reflectors working on particular frequencies in fixed directions and suspended from self-supporting steel towers some 200 feet in height.

The original high power thermionic valve rectifiers were soon replaced by much more efficient mercury vapour and later mercury arc types. Demountable valves were also introduced in the final high power amplifiers. The demountable valve, as its name may suggest, could be dismantled into its separate parts so that any component, e.g.; Filament, grid, screen grid could be replaced when a failure occurred. The components mentioned were rigidly mounted on the valve 'head' which in turn was affixed to the unit, the complete assembly being then carefully sealed at the joints, using bitumen for the more permanent joints and plasticine treated with special grease for the others. The assembled valve was continuously evacuated by means of two oil condensation pumps in cascade, backed by an oil immersed rotary pump evacuating to atmosphere. The pumping equipment was capable of creating a vacuum pressure of 10-6 mm Hg.

In this type of valve water-cooling was necessary on the filament and grid seals as well as on the anode. The oil condensation pumps were also water cooled. A valve of this principle using 18 grid filament assemblies set in a single anode jacket and devised for use on the long wave transmitter GBR and operated successfully for some time, taking the place of one power panel.

By 1937 sufficient advance had been made in the design of oscillators to permit the use of single sideband working on high frequencies and this type of communication was introduced on the high frequency TAT service in 1938.

During the war years the station suffered two major setbacks, the first being at the end of January 1940, when during a severe prolonged ice storm, the aerial became heavily overloaded with the weight of the ice forming on it. Normally the release gear at the mastheads would have catered for this eventually by automatically lowering the aerial and thereby easing the strain. Unfortunately the automatic slipping gear had frozen so solidly as to be unable to operate and the aerial finally gave way under the strain.

Very low fog persisted for some days frustrating efforts to investigate and carry out repairs and when at last it was possible to see the aerial it was found that the extent of the
damage was great. Many of the spreaders were distorted or broken beyond repair, insulators were shattered and almost a complete aerial rebuild was necessary.

The second disaster was of greater magnitude and occurred one evening in March 1943, when without warning, the woodwork on the roof of the main station housing the VLF Transmitters became ignited due to the radiation effect from GBR. Within a very few moments the whole roof was ablaze and despite the efforts of the staff and many fire brigades the transmitting room was almost gutted. Although very heavy high winds prevailed at the time it was found possible to isolate the fire to the main transmitting room and so the major damage was suffered only by the transmitters, the power equipment remaining untouched.

For some time past uneasiness had been felt concerning the vulnerability of the station to damage from enemy action, and to off-set this another radio station housing a counterpart to GBR had been set up in North Wales. This station was nearing completion at the time and by salvaging some equipment from GBR it was possible to resume the VLF transmissions from this site within a few days of the fire. The results achieved by the new station were found to be far below those of GBR and the Admiralty expressed great dissatisfaction.

The main building after the fire

The rebuilding of GBR was therefore given top priority and six months later the familiar callsign was again being broadcast around the world.

The Long Wave TAT Transmitter was also rebuilt and modernised to some extent also the Low Power Transmitter GBV which had suffered relatively little damage was also restored to service after slight modification.

During the rebuilding and re-equipping of the Main Building, the opportunity was taken to install a standby plant to supply power in the event of a total failure of incoming supplies. This was a directly coupled 1,150kW AC generator driven by a six cylinder blast injection "Fraser&Chalmers" diesel engine running at 300 rpm.

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