I have been asked to repair a clock with a radio-controlled MSF quartz movement because it keeps trying to reset itself even when it is showing the correct time.

Accordingly, I have decided to dig into the technology a little.  The National Physical Laboratory is responsible for the UK time standard which it maintains via some Caesium ‘Atomic Clocks’.

I won’t go into how an atomic clock works, except to say that caesium atoms placed in a special ‘oven’ can be made to vibrate at an extremely consistent frequency, i.e. number of vibrations per second.  By counting the vibrations, you can measure the interval between two events, and a second is now defined as a particular number of vibrations of the atom.  This is regarded as one of the most fundamental units of measurement.

This allows us to measure the time between noon on successive days. As discussed elsewhere in these blogs, this varies slightly throughout the year and from year to year, due to complex astronomical factors. In the Victorian era, it was decided to average these fluctuations to give a consistent length of 24 hours (86,400 seconds) to each day, and this was formerly known as Greenwich Mean Time or GMT.  Noon was the instant that the sun was at its highest elevation in the sky above Greenwich, but averaged throughout the year.  Owing to perhaps internationalistic concerns, it was decided to rename GMT as UTC – Universal Coordinated Time (presumably the word order is different because it was defined in French!)

So the atomic clocks at the NPL are calibrated to show UTC. In fact, to keep UTC in synch with the sun, it is occasionally necessary to add a second to the length of the day from year to year.

There has to be a way of allowing people to set their clocks to the universal time.  Originally, you had to take your chronometer to Greenwich and to set it from the reference clock which is (still) at the gate there.  Then there was (and still is) the Greenwich time signal which is broadcast by various radio stations, although I’ve noticed much less so nowadays.  The reason is that digital radios have built in processing delays, so the pips can often be randomly delayed by a number of seconds, which is not good for an accurate clock.

The solution was to build a huge special radio station at Anthorn, near Carlisle, on the site of a wartime aerodrome.  This houses an atomic clock synchronised to UTC (probably it defines UTC!) and broadcasts a time signal on a frequency of 60 kHz.  This is an extremely low frequency for a radio signal – very long wave length of 5 km!!  I won’t go into how the aerial is matched to this frequency as it needs an understanding of radio technology.

The 60 kHz carrier acts as a national frequency standard and it is modulated by on-off keying to transmit the time information, which can be decoded using standard software. The transmission power is 17 kW, which produces a useable signal throughout northern and western Europe.

The call-sign is MSF which is not an abbreviation of anything in particular, although it is sometimes called ‘Master Standard Frequency’.

Some radio controlled  quartz clocks are use the German DCF77 signal, which is said to be useable at up to 2000 km distance.

So radio controlled quartz clock movements for use in the UK will be designated as MSF or DCF.  However, it should be noted that German time is 1 hour ahead of UK time, and summer time (daylight saving time) corrections whilst currently synchronised across Europe, may not remain so.  It is therefore advisable to ensure that when you buy a movement for use in the UK, you ensure it is designed to receive MSF.

A lot of the quartz movements are designated UTS, which puzzled me for a while – I wondered if it was some sort of manufacturing standard, but it now seems that it is a German brand name of clock.