Time from NPL (MSF)

The Time from NPL is a radio signal broadcast from the Anthorn Radio Station near Anthorn, Cumbria, which serves as the United Kingdom's national time reference. The time signal is derived from three atomic clocks installed at the transmitter site, and is based on time standards maintained by the UK's National Physical Laboratory (NPL) in Teddington. The service is provided by Babcock International (which acquired former providers VT Communications), under contract to the NPL. It was funded by the former Department for Business, Innovation and Skills; as of 2017^[update] NPL Management Limited (NPLML) was owned by the Department for Business, Energy and Industrial Strategy (BEIS), and NPL operated as a public corporation.

The signal, also known as the MSF signal (and formerly the Rugby clock), is broadcast at a highly accurate frequency of 60 kHz and can be received throughout the UK, and in much of northern and western Europe. The signal's carrier frequency is maintained at 60 kHz to within 2 parts in 10¹², controlled by caesium atomic clocks at the radio station.

A radio station at Rugby was first operated by the Post Office from 1926, with the call-sign GBR. From 19 December 1927, it broadcast a 15.8 kHz time signal from the Royal Observatory which could be received worldwide. It consisted of 306 pulses in the five minutes up to and including 10:00 and 18:00 GMT, with a longer pulse at the start of each minute. Frequency-shift keying was added in 1967, making the signal harder to use as a frequency reference. The time signals, preceded by the callsign "GBR GBR TIME" in Morse code, were transmitted during the 5 minutes preceding 03:00, 09:00, 15:00 and 21:00. Transmitter GBZ on 19.6 kHz was used as a reserve, when GBR was off-air for maintenance. Eventually, time signals from GBR were terminated in November 1986 and it is no longer used as a frequency reference.

The MSF signals started in 1950, following the transmission pattern described below. They were originally intended to provide frequency references at 2.5, 5 and 10 MHz, originally only occasionally during the day. At first, there were announcements every fifteen minutes, beginning with the Morse code representation of "MSF MSF MSF" (MSF is "-- ··· ··-·" in Morse code), followed by speech "This is MSF, Rugby, England, transmitting ...". From May 1953, the signal was broadcast 24 hours a day, but with regular five-minute stoppages to allow the reception of other signals. The 60 kHz signal finally became an uninterrupted 24-hour service in 1966, and the frequency references were discontinued in February 1988.

On 27 February 2007 the NPL started tests of the new time signal transmissions from Anthorn. The Anthorn station was operated by VT Communications from its opening in 2007 until 2010, when it was acquired by Babcock International.

The formal inauguration of the relocated facility took place on 1 April 2007, when the name of the service became "The Time from NPL" and the signal from Rugby was permanently switched off. The change in location and consequent change in signal strength can make some equipment designed to use the MSF signal fail to continue doing so. This is found more in domestic equipment not designed for optimum sensitivity and positioned haphazardly.^{[citation needed]} Currently, the signal from Anthorn is still usable as far as the Mediterranean, although it is weaker than Rugby.

From the time signal's inauguration in 1950 until 1 April 2007 it was transmitted from Rugby Radio Station near Rugby, Warwickshire. The transmitter's original location meant that the clock was referred to as "the Rugby clock". Following its relocation in 2007 to Cumbria, the NPL now formally calls the signal "The Time from NPL".

The Rugby transmitter's callsign was MSF, where 'M' is one of the ITU prefixes allocated to the United Kingdom, and the letters 'SF' were allocated for no documented reason. This resulted in the common terminology "the MSF signal", which is still used by the NPL. The official history of the service says that "Rugby was given an additional commitment for the transmission of reference Modulated Standard Frequencies", but no actual explanation is given for the call sign "MSF". According to the NPL it seems the call sign was chosen so that it could be memorized as "Master Standard Frequency" but MSF was not intended to be an abbreviation.