SiteName: Rugby Radio Station
[Source: Malcolm Hancock]
OFFICIAL HISTORY OF RUGBY RADIO STATION
FURTHER DEVELOPMENT ON HF AND POWER
A two-fold plan was followed in designing the building. First the low power equipment, the high power equipment and the aerial switches were segregated in different parts of the building and secondly, a large measure of automatic control and monitoring was introduced centred at a Central Control Position making the station easy to operate and of pleasing appearance.
One large room houses the drive equipment for telephony and telegraphy,
the carrier oscillators, the automatic monitors and the landline equipment.
The transmitters are air cooled and installed in three halls converging
on the Central Control Position, from where, by remote control, any
transmitter can be operated on any one of six
Most of the aerials are three wire rhombics, many of which are mounted in pairs one above the other 150 feet and 75 feet above the ground on light lattice masts of the Post Office No 1 type. Four Koomans arrays were set up on three 325 feet masts especially for use on the New Zealand service.
In some cases switches were fitted at the base of the aerials to permit the direction of transmitted signal to be reversed or dephased by remote control from the Central Control Position. The monitoring is so arranged that continuous comparison is made between the incoming and outgoing telegraph signals, and when on telephony any variation of greater than 3db in carrier power level will indicate a fault. Reflectometers are situated in the aerial feeders and constantly measure the voltage standing wave ratio at the output of the transmitter. Should this at any time exceed a predetermined ratio of 2:1 the transmitter will automatically be shut down to prevent damage and an alarm signal will be given at the Central Control Position.
The new station or ("B" Building) was put into operation in 1953 and after its completion attention was given to the refurbishing of the original Short Wave "A" Building. The majority of the transmitters in this building were relatively inefficient and somewhat limited in performance and arrangements were made to scrap nine of the oldest units and replace them by twelve modern more powerful air-cooled transmitters. They were of a different make and design, type DS13, manufactured by "ST&C". They provided similar facilities to those already installed in the "B" Building and allowed a fair measure of automation and Central Control to be introduced into the "A" Building also.
The one real point of difference in the transmitters installed in the
"A " Building was that they have an unbalanced 75. output
and so are not able to make use of exponential line
The half wave element aerials originally associated with the "A"
Building were mostly dismantled and replaced by the more versatile rhombic
which, while not having the high gain of the array, are less critical
as to frequency and have good directional properties.
The large d.c. generators supplying the EHT supplies to the two high
power VLF transmitters had now begun to require more frequent attention
and were being regarded as a possible maintenance liability. It was
decided therefore that the d.c. machines
The new engines are English Electric type 12SV with 12 hour rating
of 1,350 b.h.p. and a 30 second rating of 1630 b.h.p. at 750 r.p.m.
The short time rating and the special heavy flywheels fitted were required
to deal with the peak loads imposed when GBR is being keyed. The complete
station is fed via a ring main by an 11kV supply from the Public Grid
and the emergency supplies can be paralleled and synchronised in and
out as required. Two further English Electric type 12SVA engines were
installed to replace the "Fraser & Chalmers" in 1967
Almost since its inception Rugby has broadcast twice daily time signals on 16kHz. In 1951, Rugby was given an additional commitment for the transmission of reference Modulated Standard Frequencies.
Suitable equipment was installed in the main Building and included three high- grade 100khz crystal oscillators to provide signals accurate to within two parts in 108 of the assigned frequency. By means of frequency dividers and multipliers carrier frequencies were obtained at 60 kHz for the Long Wave Telephony Transmitter (the GBT/GBY TAT service by now having ceased) and 2.5, 5, 10, 15 or 20 MHz for three of a set of four HF ST&C ES4A transmitters which were newly installed for the purpose.
The equipment also provided for continuous intercomparison and recording of the frequencies of the master oscillators in pairs, so that any divergence from normal on the part of any one the oscillator chains might be detected and corrected. Continuity of operation being an essential feature of a Frequency Standard of this kind, the master oscillators were fully protected against any interruption of the power supplies.
In the first instance the crystals were quartz resonators cut in the GT mode but were later replaced by the Essen Ring type suspended on silken cords and giving a higher degree of stability. The carrier and modulation frequencies were all derived from the crystal oscillator which was regulated with reference to a caesium resonator at the National Physical Laboratory (NPL)
At the introduction of the service the signals were radiated continuously on a 24 hour program using carrier frequencies of 2.5, 5 and 10 MHz and for one hour on 60 kHz. Except in a small region adjacent to Rugby where the ground wave predominates the HF signals are received after reflection in the ionosphere.
Variations in ionospheric conditions can cause significant fluctuations in the received carrier frequencies at HF, thus limiting the accuracy of the MSF emissions on short waves. This problem, together with a reduction in usage, lead to the HF services ceasing in 1988. LF and VLF transmissions are not subject to these same limitations and so the 60 kHz transmission was soon found to be in great demand and coverage was extended to 24 hours daily. This high stability of transmission possible in the LF and VLF ranges began to assume great importance in other fields also and soon new uses were found for the three original transmitters which at that time seemed largely to have outlived their usefulness.
The MSF Standard was arranged to generate the carrier frequency of the GBR transmitter but it was found that there was phase shift inherent in the transmitter due to the magnetic attraction between the aerial tuning coils creating movement of the inductances when the transmitter was being keyed. This movement was overcome by enclosing the windings of the inductances in paxolin sheaths and automatic phase correction was also introduced. The transmitter was then restored to service with greatly increased stability of transmission.
At about this time tests had also been carried out on 68 kHz (GBY) using various methods of keying the outcome of which was that the transmitter was used for a 24-hour teleprinter service. To make the transmitter available for this service the Medium Power LF transmitter was retuned from 78kHz to 60kHz and took over the MSF transmissions on LF.
In view of the great importance attached to the VLF transmissions on GBR it was decided to rebuild the transmitter using more modern equipment and with increased power output. The new transmitter, completed in 1967, was designed and constructed by the Post Office Engineering Dept.
The new transmitter has retained the original aerial, tuning and power equipment, while the water cooled valves previously employed have been replaced by three vapour-cooled amplifier valves for use singly or in combination. The modulator circuitry has been redesigned so that frequency shift as well as C.W. signals can be generated at speeds up to 72 baud.
Also in 1967 the Essen Ring oscillators were superseded by the installation of Rubidium Vapour Standards to permit frequencies accurate to 1 part in 100,000,000,000 (1 second in 3,000 years) to be radiated.
The 24 hour 60kHz MSF standard frequency service that commenced in 1966 was originally on a new 50kW "Marconi" type H1211 transmitter, however, in 1974 it moved back to the GBY transmitter which had been completely modernised by the Post Office Engineering Dept. in 1972.
This was also the same year in which the first time code was radiated. On 18th December 1998 the service moved yet again to a new solid state "Telefunken" transmitter. This substantially improved the electrical efficiency and also enabled maintenance outages to be reduced from monthly to quarterly.
The MSF 60kHz transmitter radiates a 24-hour time signal service and
is the principle means of disseminating the UK national standards for
time and frequency.
The original 100Hz time code ceased on 7th October 1998. Today the
station has a suite of three standards, two caesium beam and one rubidium
vapour. The transmitted frequency and time code are derived from these
atomic standards which enable the
Three chains are required not only for reliability of service, but for triangular intercomparison. Readings are taken daily to compare the accuracy of the Rugby standards with those at the NPL at Teddington.
UP TO DATE
The move from point-to-point services to long range maritime/mobile
operations on High
Most of the rhombic aerials were replaced with "spiracone" inverted cone and stack quads omni-directional type, plus three, motor driven, steerable log periodic aerials. These long-range services are controlled by operators at Burnham-on-Sea (well known by most mariners as "Portishead Radio"). The receivers for the service being located at Somerton Radio Station in Somerset. These services, using Morse, teleprinter/telex or voice, are capable of connecting a ship anywhere in the world directly back to the UK for onward connection, if required, to any other country in the world.
A reduction in maritime traffic allowed all the services to be concentrated in Rugby 'B'. Therefore the 'A' Building closed as a transmitting station in the early nineties and BT Group Records and Information Services (GRIMS) converted it for use as a document storage facility.
The HF Maritime service at Rugby 'B' Building finally ceased at the
end of April 2000.
Most of the 'B' Building now houses a customer service centre for mmO2 Airwave, an exciting new "Public Safety Radio Communications Project".
The special applications found possible due to the particular propagation properties of the LF transmissions, seem to indicate that the future of some of the long wave transmitters, such as the MSF 60kHz "Time Signal" service, are assured for many years to come.
Rugby Radio Station is at the heart of BT Radio Services design, maintenance
and support facility providing a wealth of expertise in an ever-changing
Have you noticed the new, brighter, aircraft warning lights installed in 1999? For most people, the 820ft masts have always been there and there is, at least, a few more years of radio history to be written before these engineering masterpieces cease to grace the surrounding countryside.
1st Edition - M. Johnstone - 1st January 1976
[Source: Malcolm Hancock]