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Globally, several national physical laboratories operate radio transmitters that broadcast a time code signal. The following transmitters operate in the 40–80 kHz range and are used to synchronise radio clocks over areas from several hundred to thousands of kilometres across. The following short synopsis is mainly concerned with the UK MSF transmitter at Anthorn, Cumbria as it is targetted for UK readers. Other countries produce similar documentation for their own standards.

• JJY: (transmitter No. 1) uses 40 kHz, 50 kW and is located on the summit of the Otakadoya-yama mountain near Miyakoji-mura/Fukushima/Japan (37° 22' N, 140° 51' E).
• JJY: (transmitter No. 2) uses 60 kHz, 50 kW, is located on the summit of the Hagane-yama mountain, near the border of the Saga and Fukuoka prefectures of Japan (33° 28' N 130° 11' E), started service October 2001.
• RTZ:     50.00 kHz, 10 kW ERP, Irkutsk/Russia (52° 26' N, 103° 41' E).
• RBU:     66.66 kHz, 10 kW ERP, Moscow/Russia  (55° 44' N, 38° 12' E).
• MSF:     60.00 kHz, 15 kW ERP, Britain (54° 55' N, 3° 15' W), received throughout much of Northern and Western Europe.
• WWVB: 60.00 kHz, 50 kW ERP, Ft. Collins/Colorado/USA (40° 40' N, 105° 03' W), received throughout most of mainland USA.
• HBG:     75.00 kHz, 20 kW ERP, Prangins/Switzerland (46° 24' N, 06° 15' E), DCF77 compatible code.
• DCF77: 77.50 kHz, 50 kW (30 kW ERP), Mainflingen/Germany (N 50° 01', E 09° 00'), received up to around 2000 km from Frankfurt/Main.

MSF Transmitter (UK)
The MSF transmitter was located at Rugby for many years until re-locating to Anthorn on 1 April 2007.

The National Physical Laboratory in Teddington produces the initial reference time (UTC), using its caesium atomic standard, and sends it to Anthorn where the local clock is synchronised to it before being broadcast as a long wave radio signal. The format is a sequence of 60 pulses, one pulse per second, each pulse constitutes a data bit. A minutes worth of data bits encodes the time and date information. The data string is terminated on the minute boundary by a marker to signify the start of a minute.

The estimated equivalent monopole radiated power (EMRP) is 15 kW and the horizontal radiation pattern is substantially omnidirectional.

The signal provides a field strength exceeding 100 microVolts/m throughout the UK, and it can be satisfactorily received throughout much of northern and western Europe and Ireland.

Is the signal continuous?

The MSF 60 kHz time and frequency signal broadcast from the Anthorn Radio Station operates for 24hrs a day but is occasionally taken off-air to allow maintenance work to be carried out in safety. These are usually of short duration and are always pre-planned well in advance (see reference to NPL site at the bottom of this page).

It is possible that short unscheduled breaks in transmission will occur in addition to the routine breaks due to unforseen maintenance. NPL provides a help line (+44 (0)20 8943 6493) which gives information on whether the MSF signal is in one of its maintenance periods, and, during working hours, whether the signal is on air.


Why is such a low frequency used to transmit time signals?

Other, high frequency, time-signal transmissions do exist (WWV and GPS, for example) but long-wave signals have a number of advantages. They can go around obstacles such as mountains or buildings. Since no line-of-sight is necessary (as it is for GPS) between the transmitter and receiver, a single station can cover a huge geographic area using a reasonable power. This provides a huge logistical and cost advantage. Long-wave signals even penetrate the walls of most brickwork buildings quite well. The technically-minded readers will be interested to know that signal propagation occurs mostly in the form of a ground wave, so that transmission delay is less affected by the variability of the ionosphere, also such low frequencies are far less affected by "multipathing", within the coverage area, or the condition known as "channel ducting" which distorts the field strength around coastlines. The net result is that a fairly even distribution of signal strength is present over the coverage area irrespective of geological variations, or man made structures.

What is the coverage of the MSF radio time code signal?

The target coverage of the MSF signal is the whole of the of the British Isles, however the time code signal can be received up to 1500km from Anthorn. This covers most of Western Europe , including the UK, Ireland, France, Netherlands, Belgium, Denmark.

What is the coverage of the DCF time signal?

The DCF radio time code signal is broadcast from Frankfurt, Germany, the coverage of the DCF signal is the whole of the Germany. The time code signal can be received up to 1500km from Frankfurt. This covers most of Central and Western Europe, including the UK, France, Netherlands, Belgium, Denmark, Switzerland and Northern Italy.

References:

www.npl.co.uk/time      Information on the generation of time signals and a history of timekeeping.

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