The MSF-60 atomic clock synchronized radio time transmission is utilised by many NTP Time Server and PC computer systems to provide accurate synchronization 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 follows: 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’.
How To Synchronize Your PC to the Rugby Atomic Radio Time Signal
The MSF-60 radio atomic clock time signal provides an accurate time reference broadcast throughout the British Isles. The time signal can be used as an accurate time reference to synchronize time on computers and computer networks. This article describes how the MSF-60 time signal can be decoded and used to synchronize computers and NTP time server systems.
The MSF radio time signal was, until recently, broadcast from Rugby, Warwickshire, where it was maintained by BT Radio Engineering. The transmitter has since been relocated to Anthorn, Cumbria, where it is now maintained by VT Communications.
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 transmission is synchronized with highly accurate atomic clocks based at the National Physics Laboratory (NPL). 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 carrier is turned off for a 500-millisecond period to indicate the start of each 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 Summer\Winter time (GMT\BST). - Software decodes for the MSF radio time broadcast is provided within the standard NTP server distribution for Linux. The NTP server software distribution has also been ported to Microsoft Windows operating systems. NTP is a standard way of synchronizing time on computers and computer networks.
A number of MSF radio receivers are detailed on various web sites. Also a number of commercial vendors offer small low-cost radio receivers that can be interfaced to a PC to receive the MSF time signal.
MSF Signal Issues
What is the maximum cable length of the MSF radio antenna ?
It’s not often that reception problems are reported, particularly with the IP66 Professional MPS unit.
Geographic location tends to be less of an issue than local environment. We have units as far north as Aberdeen, as far south as the Channel Islands and also in Ireland.
A few things worth trying:
The MSF time signal is transmitted from Rugby in the East Midlands, UK.
The MSF radio antenna is a unidirectional antenna which ideally needs to be mounted horizontally, perpendicular to the source of the radio transmission. For the IP66 unit, hold the antenna in an upright position with the cable exiting the bottom of the antenna, point the face of the antenna in the general direction of Rugby.
The NTP Time Server antenna needs to be mounted above ground away from any sources of electrical interference. Metal structures can act as a Faraday cage blocking signal penetration. Therefore, the antenna must be located externally of any metal structures.
Removing the lid of the antenna reveals a LED. When powered, the LED will light green. When the antenna has a lock on the time signal, it will flash red / green. The antenna should be re-located or rotated until a regular 1 second pulse is obtained on the LED. If the LED flickers irregularly or does not flash, the antenna must be repositioned.
Failing this, to test operation, it could be worth trying the unit in a completely different location on a completely different PC. Ultimately, however, synchronization does depend on the radio signal being present. Failing this, a GPS solution may be worth considering. The upside to GPS is that a signal lock can be guaranteed, the down-side is that ideally the antenna needs a good view of the sky.
MSF Synchronization Accuracy
The MSF radio time signal is available throughout the British Isles and most of Western Europe. Broadcast time and date information is repeated every minute with a marker at the end of each minute. The accuracy of the end of minute marker is ± 1 millisecond (one thousandth of a second).
The NTP s5000 series NTP Time Server can synchronize time with the MSF radio transmission to an accuracy of ±1.4 milliseconds.
MSF Radio Antenna Location
Where is the best place to locate a MSF radio antenna ?
Generally, the MSF radio time signal can be received indoors close to the host NTP Time Server. However, there are a number of things can can interfere with MSF time signal reception.
1. If the antenna is sited underground or on a basement. Ideally the antenna should be located above ground.
2. If the antenna is sited inside a metal cage. Metal cages, such as racks or metal building cladding can weaken the MSF signal strength. The signal may still be received satisfactorily, but ideally the antenna should be located outside any metal cage
3. If the antenna is located too close to electrically noisy equipment. If the antenna is located on top of a PC monitor for instance, it will tend to drown the signal out. However, move the antenna a couple 50-60cm away and generally it is fine.
MSF Radio Transmitter Relocation
The contract between NPL and BT for the transmission of the MSF-60 radio time signal expires in March 2007. After March 2007, VT communications will take over a replacement service.
This means that the radio time transmissions will be broadcast from Anthorn, Cumbria, rather than Rugby.
At the end of 2006, the Rugby transmitter will be switched off, periodically, for a number of tests on the Anthorn transmitter to ensure correct operation and that the service is performing as expected. After March 2007, the Rugby signal will be switched off and replaced by the transmitter located at Anthorn.
MSF Antenna Cable Requirements
What is the maximum cable length of the MSF radio antenna ?
The Low-cost MLS MSF Radio Antenna is supplied with 2m of cable. This can be extended to 12m using a standard RS232 9-way D type serial extender. This is a straight through RS232 cable with 9 way male to 9 way female.
The IP66 Professional MPS MSF Radio Antenna is also supplied with 2m of cable. However, this can be extended up to 100m from the NTP time server using CAT3, 4 or 5 point to point structured cabling or alternatively using CAT5 patch lead.
What is the signal coverage of the MSF radio transmitter ?
The MSF radio time code signal is broadcast from Rugby, UK, the coverage of the MSF signal is the whole of the of the British Isles. The time code signal can be received up to 1500km from Rugby. This covers most of Western Europe , including the UK, Ireland, France, Netherlands, Belgium, Denmark.
MSF Signal Outages
The MSF radio signal broadcast from Rugby, UK, has annual maintenance periods whereby the signal may be taken off-air for short periods of time.
What advantages are associated with using the MSF radio time transmitter ?
The MSF-60 radio time signal transmission is broadcast from Anthorn, Cumbria. The coverage of the MSF-60 signal is the whole of the British Isles and Ireland. The MSF radio time signal can also be received throughout much of Western Europe, including the Channel Islands.
The advantage of radio signal reception over GPS is that generally a good signal can be received indoors close to the host computer or time server. GPS ideally requires a roof mounted antenna, which can be inconvenient and expensive.
Is the MSF Signal Affected By Weather
The MSF radio time signal transmitted from Rugby is not affected by weather conditions. Poor weather conditions cannot corrupt or alter the time code transmissions. Very brief interruptions in the radio time signal can occur as a result of ground currents generated by a local lightning strike.