Science Questions

Why are my radio controlled clocks not syncronised?

Sun, 2nd Dec 2007

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David, Harlow asked:

I have two radio-controlled speaking clocks that are identical but one’s two year’s older than the other. They speak at different times. Why is that?


We're actually not sure about this one!

Most radio-controlled clocks update themselves once a day, but cann't do so if they can't receive a strong enough radio signal.  It's possible that one of the clocks has a weaker antenna, and so isn't receiving a signal, and has fallen out of time.

Please let us know if you can think of any other reason for this!


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I assume the clocks are in different rooms, if this is so, then possibly the signal is being lost as it goes through the extra walls...or if the second radio is in a room near an outside(metal) garage, this may interfere with the signal!!!, Tue, 4th Dec 2007

He could always do the experiment, swap the clocks around and see if this changes which clock speaks first. This would give plenty of information, no matter what the result was., Tue, 4th Dec 2007

Most radio-controlled clocks have a button you can press to force them to receive the signal "on-demand" (it usually takes about 3 minutes). Normally the clock display shows whether this was successful or not.

Note also that such clocks use an internal ferrite rod antenna, which is directional, to receive the time signal. Consequently the orientation of the clock may also affect whether it can receive the signal or not. If a clock "looses" the radio-signal, it will gradually drift out of time like any other ordinary clock.

The UK time signal used to be transmitted from Rugby, but in the spring of this year (1st April 2007) was relocated to Anthorn in Cumbria (near the Scottish border). Consequently the signal-strength in the south of the UK is weaker than it used to be and so reception may now be more marginal in Harlow.

See also:

The NPL have a page about "Common Clock Problems" at
- it's probably particularly worth making sure your clocks are not close to sources of interference like fluorescent or low-energy lightbulbs if they will be switched on at the time of day the clock synchronises itself (see the clock instructions) techmind, Tue, 4th Dec 2007

How far apart are the times?

The question seems to refer to the clocks speaking at different time, but does not indicate they show different time - although it neither explicitly suggests that they show the same time, but it does seem something of a significant oversight to mention they speak at different time but not to mention they actually show different times. another_someone, Wed, 5th Dec 2007

Andrew, what band would the transmitted frequency be?, Wed, 5th Dec 2007

The web page referenced states that the MSF signal in the UK is at 60KHz.
another_someone, Thu, 6th Dec 2007

i went to the place in denver. you can go in usually and see the clocks, but they were closed. kdlynn, Thu, 6th Dec 2007

Thanks George, i guessed it was either lw or mw, but it's always nice to know rather than guess, Thu, 6th Dec 2007

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