The clever bit is that these clocks checks the radio signal with the MSF signal transmitted from Cumbria which is accurate to 1000ths of a second a year. It automatically checks itself, so that it is never wrong! It automatically changes itself to GMT and British Summer Time.
Some manufacturers refer to their radio controlled clocks as "atomic clocks", which isn’t really true. An atomic clock has an atomic oscillator inside (such as a cesium or rubidium oscillator). A radio controlled clock has a radio inside, which receives a signal that comes from a place where an atomic clock is located.
MSF Radio Time Signal The MSF radio signal is a dedicated time broadcast that provides an accurate and reliable source of UK civil time, based on the NPL time scale UTC(NPL). It is available 24 hours a day across the whole of the UK and beyond. The signal operates on a frequency of 60 kHz and carries a time and date code that can be received and decoded by a wide range of readily available radio-controlled clocks.
The MSF signal is transmitted from Anthorn Radio Station in Cumbria by VT Communications, under contract to NPL.
The antenna at Anthorn is at latitude 54° 55' N, and longitude 3° 15' W. The radiated power is typically around 17 kW and the horizontal radiation pattern is substantially omnidirectional. The signal provides a field strength exceeding 100 µV/m at a distance of 1000 km from Anthorn, which covers the whole of the UK, and it can be satisfactorily received throughout 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. The broadcast signal is monitored against the national time standard at the NPL site in Teddington and corrected when necessary, allowing it to be used as a frequency reference. Companies that need traceability from the MSF carrier frequency to UTC(NPL) and UTC can subscribe to the NPL Monthly Bulletins. MSF Time and Date Code
The MSF signal carries time and date information that is transmitted in a simple binary-coded decimal format by on-off modulation of the carrier. The full sequence of information is transmitted each minute, using two data bits during every second of the minute except the first.
The MSF time and date code includes the following information: year month day of month day of week hour minute British Summer Time (in effect or imminent) DUT1
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