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How To Decode The MSF-60 Radio Time Signal

By David Evans

Republish: EasyPublish™
Published: 17Feb2007
Word count: 436
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The MSF-60 atomic clock synchronised radio time transmission is utilised by many NTP Time Server and PC computer systems to provide accurate synchronisation of time critical applications. This article describes how the MSF-60 time signal is decoded by NTP Time Server and computer systems to provide an accurate timing reference.

The MSF-60 Time Transmitter

The MSF-60 time signal is a long-wave radio time signal broadcast from Rugby, Warwickshire, England. The radio signal is maintained by BT Radio Engineering Services under contract from the National Physics Laboratory (NPL). From 1st April 2007 the MSF-60 transmission will transfer to Anthorn, Cumbria, using atomic clock and time code equipment provided by VT Communications.

When decoded, the MSF-60 time signal provides a highly accurate timing reference for NTP Servers, clocks and other computer timing equipment.

Signal Coverage

The MSF-60 radio time signal broadcast can be satisfactorily received throughout the British Isles and much of North-West Europe. Reception problems can generally be attributed to local environmental conditions. The radio signal can be blocked by metal structures or frames, which act as a Faraday cage. Additionally, signal reception can be difficult near electrically noise equipment. Radio receivers should also be located above ground.

The MSF-60 Time Code

Time and date information is transmitted continuously, repeated each minute. The data is transmitted as on-off carrier modulated, pulse-width coded data signal. Each data bit 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.

A 500-millisecond carrier off period indicates the start of each minute. The other 59 seconds consist of between 100 and 300 milliseconds carrier off and at least 700 milliseconds of carrier on.

Transmitted Data.

Time and date information is presented in BCD (Binary Coded Decimal) format and is encoded as follows: bits 1-16 are used to convey information about the difference between atomic and astronomical time (DUT1).

The remaining bits, 17 to 59, contain date and time information about the current minute as follow: bits 17-24, BCD encoded year (00-99); bits 25-29, BCD month of year (01-12); bits 30-35, BCD encoded day of month (01-31); bits 36-38, BCD encoded day of week (0-6, 0 = Sunday); bits 39-44, BCD encoded hour (00-23); bits 45-51, BCD encoded minute (00-59).

During British Summer Time, bit 58 is set to ‘1'. Also in the 60 minutes leading up to a change in British Summer Time, bit 53 is set to ‘1'.

Dave Evans develops NTP Time Server synchronisation systems to ensure accurate time on PC’s and computer networks. Dave has been involved in the development of dedicated NTP Time Server systems, NTP synchronised digital wall clock systems and atomic clock time synchronisation products. Click here to find out more about SNTP and NTP Time Server Systems.

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