The Rugby Time Signals (GBR & MSF)


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The Rugby Radio Transmitter, which was run by the Post Office, became operational on 1 February 1926. Just under two years later, on 19 December 1927, it began the twice daily transmission of rhytmic time signals to enable sailors to check their chronometers with great accuracy. Generated by the Shortt Free Pendulum Clocks of the Royal Observatory, the signals were sent via a land-line to Rugby where they were broadcast on a frequency was 16 KHz under the call-sign was GBR. By 1944, the signals were no longer being produced by the Shortt Clocks, but by phonic motors under the control of the Observatory's newly acquired quartz clocks.

On 1 February, 1950, as well as the GBR signals, Rugby also started broadcasting standard frequency transmissions under the call sign MSF on a frequency of 60 kHz. The clocks that produced the signals were not at the Observatory, but at the Rugby transmitting station itself and were overseen by the National Physical Laboratory (NPL). Initially the transmissions lasted from 1030 to 1045 each day?? [check this]. As well as being monitored by NPL they were also monitored at Abinger and the results communicated daily to the Post Office Radio Branch.

In 1960, the Astronomer Royal reported that:

'Agreement has been reached between the Royal Greenwich Observatory, the National Physical Laboratory, and the Post Office for the co-ordination of the radio time signals transmitted by Rugby GBR and its associated short-wave transmitters with the MSF standard frequency transmissions. Both series of signals will now be controlled from the same equipment at Rugby and will of course still be monitored by the Observatory; as a result, the land-line to Rugby is no longer required. The Royal Greenwich Observatory retains the responsibility for the time signals, and the National Physical Laboratory for the frequencies: maintenance and operation of the equipment will be the responsibility of the Post Office.'

In 1966, the transmission times for the MSF signals were increased to 24 hours a day. Publication by the Observatory of GBR and MSF phase results ceased in June 1985. The transmission of the GBR signal was discontinued in the summer of 1986. In 1987, transmission of the MSF signals was moved from Rugby to Anthorn, from where they continue to be transmitted today.

Standard frequency transmissions from the United Kingdom. Nature (1958)



The following notice was released by the Admiralty on 26 September 1927 (from Radio Service Bulletin, Washington):

‘It is intended during the month of December, 1927, to inaugurate a service of wireless time signals at Rugby radio station, which will be broadcast twice daily – at 10h. and 18h., G. M. T.

The time signal will be of the modified rhythmic type recommended by the International Time Commission of 1925. It will comprise a series of 306 signals emitted in 300 seconds of mean time (or, alternatively, 245 signals emitted in 240 seconds of mean time), the concluding signal being the exact hour.

In each series, signals Nos. 1, 62, 123, 184 and 245 (and 306, if the series extends for five minutes) are single dashes (-) of 0.4 second duration and commence at the exact minute. Each dash is followed by 60 dots (.) of 0.1 second duration.

The commencement of successive signals, whether dot or dash, are equally spaced at intervals of 60/61 parts of one second of mean time.

The intended procedure will therefore be as follows:


m. s.

55 00 1st signal, a dash (-) followed by 60 dots (.... etc.).

56 00 62d signal, a dash (-) followed by 60 dots (....etc.).

57 00 123d signal, a dash (-) followed by 60 dots (.... etc.).

58 00 184th signal, a dash (-) followed by 60 dots (.... etc.).

59 00 245th signal, a dash (-) followed by 60 dots (.... ..etc.).

00 00 306th signal, a dash (-).

This type of time signal will enable chronometer comparisons of extreme accuracy to be obtained, the method employed being to count the number of intervals from the first dash (-) until coincidence occurs between one of the rhythmic signals and the beat of the chronometer. It is not necessary actually to count the signals. Take the nearest second of each dash by the chronometer and write down the chronometer time of coincidence. The difference gives the number of the rhythmic signal,

For ordinary navigational purposes a comparison obtained by disregarding the dots and using the commencement of the dashes only (given at the exact minute) will be sufficiently accurate. Call signal, GBR, wave length, 18,740 meters, c. w.; location (approximately), 1° 11’ W., 52° 22’ N. – Admiralty, London, Notice 1643, September 26, 1927.’

The wavelength of 18,740 metres corresponded to a frequency of 16 Kc/s or 16 KHz.



Website Radio Station Rugby

Press release about the relocation of MSF transmissions from Rugby to Anthorn (archived from the original)


Extracts from the National Physical Laboratory Reports for the years 1949 1959 and 1967 relating to the MSF transmissions.

The extracts below are taken from the following reports

National Physical Laboratory Reports for the years 1939–1953

National Physical Laboratory Report for the year 1967



During the year it was decided that a national service of standard radio transmissions shall be established and that the Electricity Division of the Laboratory should accept responsibility for the actual standard of frequency, though the transmissions will be made from Rugby by the General Post Office. In order that all the preparatory work should be completed by the end of the year, a good deal of work has been concentrated on this item; equipment for the automatic reception and measurement of the various frequencies required has been constructed, and there is every prospect of a service on a limited scale being in operation early in 1950. These early transmissions will, of course, be to some extent experimental, in the sense that they will indicate to what extent the service will meet needs that are at present unsatisfied, how far they can be expected to yield scientific information concerning the process of transmission, and to what extent interference between British and American transmissions is likely to occur when a more complete system is established. These matters will receive attention in the coming year.



The service of standard frequency transmissions has been in operation since 1st February, 1950. The transmissions are made from the Post Office station at Rugby and monitored at the Laboratory. Over a period of a day the frequency transmitted has been found to remain constant to about 1 part in 109. There is of course a slow drift of frequency which is corrected whenever the deviation from the nominal value approaches 2 parts in 108, but such corrections have only been required about once a month. Reports of the reception of the higher frequency transmissions are being received from many parts of the world and in due course a clear picture of the areas covered by these transmissions and of the areas in which there is interference between them and the transmissions from Washington should emerge. At present the information is inadequate, probably because of the relatively short daily period of the new transmissions, which is to be increased as soon as transmitters become available.



Plate 1 Quantum Metrology

The NPL is responsible for the standard frequency and time signal transmission service of the United Kingdom which is operated by the External Telecommunications Executive branch of the GPO. Introduced in 1950 and identified by the call-sign MSF, this service is radiated from the group of transmitters at Rugby Radio Station. Here the NPL, as part of its responsibility for controlling frequency standards, has installed new atomic frequency equipment during the past year at a cost of approximately 10 000. The MSF transmissions, the running cost of which is 40 000 a year, make an important contribution to science and industry by providing reference standards of frequency of high accuracy over a wide area of the British Isles through the medium of radio communication. The photograph shows Dr. A. H. Cook and Dr. L. Essen (NPL) in conversation with Mr. C. W. Sowton (GPO-ETE) at the formal handing - over of the atomic frequency installation to the staff of the radio station. (Photograph by courtesy of H. M. Postmaster General)


[P.4 &5]. The frequency standard is made widely available by means of standard frequency transmissions and a service, having the call sign MSF, has since 1950 been operated by the Post Office on behalf of the NPL from the Rugby station . Although the frequencies have been monitored at the NPL the transmitters were controlled by standards at Rugby which were installed and maintained by the Post Office Dollis Hill Station. The standards used were Essen quartz rings of Dollis Hill manufacture and they enabled the transmitted frequencies to be maintained within a few parts in 1010 of their nominal values. Such a high accuracy could be fully exploited only by use of the LF (60 kHz) transmission and this was for many years the most accurate transmission in the world. Since 1960 it has operated for 24 hours per day.

In 1967 the NPL accepted responsibility for the MSF standard equipment at Rugby and at the same time some changes were made. In the first place, the quartz standards have been replaced by rubidium gas - cell atomic standards which have a day-to-day stability of + 1 part in 1011 and a yearly stability of about 1 part in 1010.

A second change of great significance is to transmit the carrier waves at their true nominal frequencies in terms of the atomic unit of time . In the past , although the atomic unit has been used , the carrier frequencies and the 1 s pulses obtained by dividing these frequencies have been offset from their true values in order to make the 1 s pulses correspond approximately to the astronomical scale of uniform time ( UT ) which is based on the rotation of the Earth . Navi gators could use the signals without correction , but the offset of frequency had to be changed from time to time to follow variations in the rotation of the Earth ; occasional step adjustments in the time signals had also to be made . The transmissions are today used for a great number of applications for most of which true atomic frequency and time would be more useful . As a first step the carrier waves now have their true atomic frequencies , but the 1 s pulses are still derived from an offset oscillator in order that they should remain on the internationally co - ordinated scale (UTC) . The amount of the offset is at present - 300 parts in 1010 but there is a proposal to change it to - 250 parts in 1010 on 1st January, 1968. If the carrier wave is used as a standard no correction is needed. If the 1 s pulses are used a correction, which may be changed each year, must be applied.

The rubidium standards do not operate at the spectral line frequency because of the presence of a buffer gas with the rubidium atoms. This is required for technical reasons, and it is not entirely a disadvantage because it enables the frequency to be set during manufacture so as to give an output at exactly 5 MHz. The offset frequency is obtained by means of an electro-mechanical device made at the NPL which produces a continuous change of phase and hence a constant difference of frequency. A signal at 100 kHz from the rubidium standard is passed through a network consisting of a capacitive phase shifter which displaces the phase of the signal applied to it by an amount dependent upon the speed of rotation of a dielectric rotor, which is between the input and output plates. The rotor is driven at a pre - set speed determined by the desired offset.

The new MSF frequency standards are the first instalment of a programme of modernisation of the standard frequency and time control equipment. Within the next year a new transmitter for the 60 kHz service will come into use which will enable the nominal power to the antenna to be increased from 10 kW to 50 kW, improving the signal strength over the service area and providing more reliable continuous operation.

A comprehensive installation of frequency monitoring equipment is in use at the Laboratory, continuously recording the phases of a number of standard frequency transmissions against the caesium standard.

The transmissions being monitored are in the VLF and LF ranges between 10–30 kHz and 60–200 kHz, which have been found to be the most stable ranges for inter-continental and continental frequency comparisons respectively. Past investigations on the propagational characteristics of VLF transmissions established their usefulness as a medium for precise frequency comparisons over distances of several thousand kilometres, and during the past year such comparisons have been in progress between the National Bureau of Standards and the National Physical Laboratory using the WWVL transmission on 19.9 kHz from Fort Collins, Colorado. The phase records have yielded some interesting information on propagational conditions from time to time, particularly with regard to the effects of solar activity, such as solar flares and polar cap disturbances.

Phase measurements on the 60 kHz transmission from Rugby are used to decide when to make adjustments to the standard controlling MSF; it has been found that because the transmission path between Rugby and Teddington is very stable the phase of the signal received at NPL is almost as stable as that of the transmitted signal. In August 1967 the NPL installed a rubidium frequency standard at the BBC transmitter at Droitwich to investigate the phase stability of this transmission and this work is still in progress.

The mean daily deviations from nominal frequency of the monitored transmissions are published monthly in the Journal of the Institution of Electronic and Radio Engineers and are available through the Laboratory's own distribution service at more frequent intervals.