The MSF radio time signal is a highly accurate time and frequency radio broadcast. The signal can be received throughout the UK and much of Western Europe. The transmission provides an accurate timing reference for many types of equipment and can be used by computers and computer networks for time synchronisation. This article describes the format of the radio broadcast and how it can be utilised by computer equipment and NTP servers for precise timing.

The MSF radio time signal was, until recently, broadcast from Rugby, Warwickshire, where it was maintained by BT Radio Engineering. The radio transmitter has recently been relocated to Cumbia, North East England. VT communications was awardedIt is now maintained.

The signal is a long-wave radio signal broadcast at 60kHz. The broadcast can be satisfactorily received throughout the British Isles and much of North-West Europe. The radio signal can generally be received indoors. However, reception problems can be caused by metal structures, electrically noise equipment or if the antenna is located below ground level.

The time signal is synchronised with precise atomic clocks located at the British National Physics Laboratory. Local time and date information is broadcast continuously, repeated each minute. The time information is transmitted as on-off carrier modulated, pulse-width encoded data signals. A series of 59 data bits make up time information and is transmitted as one pulse per second. The data transmitted consists of the current time and date, leap second indicator, daylight saving time indicator and parity bits.

The signal breaks for a five hundred millisecond interval to indicate the begining of the minute. The other 59 seconds signify data bits and consist of between 100 and 300 milliseconds carrier off and at least 700 milliseconds of carrier on.

Time information is broadcast in Binary Coded Decimal (BCD) format and is encoded as described below.

Bits 1 to 16 are used to convey information about the difference between atomic and astronomical time (DUT1).

Bits 17 to 24 provide the BCD encoded year in the range 0 to 99.

Bits 25 to 29 provide BCD encoded month of year information in the range 1 to 12.

Bits 30 to 35 provide BCD encoded day of the month information in the range 1 to 31.

Bits 36 to 38 provide BCD encoded hour in the range 0 to 23.

Bits 45 to 51 provide BCD encoded minutes in the range 0 to 59. Bit 58 indicates British SummerWinter time (GMTBST).

Software decodes for the MSF radio time broadcast is provided within the standard NTP server distribution for Linux. The standard NTP distributions has also been adapted for the Microsoft Windows operating systems and is available from the NTP website. NTP is a standard way of synchronising time on computers and computer networks.

A number of MSF radio receivers are detailed on various web sites. Also, low-cost radio time code receivers that can be connected to a PC serial port are available from a number of commercial vendors. These allow the time signal to be received and decoded by a standard PC.