How Radio Controlled Watches Sync with Atomic Clock

Hello guys,

I've always been curious about how things within my vicinity actually work, it makes me discover and learn new stuffs every day. I thought this would be a very Interesting topic to expound upon today. You may have gone to any store and find watches that automatically set themselves and they all claim that it will be accurate within one second for millions of years.

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A lot of these watches aren’t that expensive, so how can such a cheap watch be so accurate?

_[2]_{A simple radio receiver}

These watches or clocks are actually as accurate as they advertised but it's not because of any piece of special tech within the watch itself, these watches all have radio receivers in them which receives a time signal so that they know exactly what time it is at all times.

Where exactly does this signal come from?

Based on my research, if you’re residing in the United States of America, you might have heard of something called “NIST” (National Institute for Standards and Technology) in Colorado and this institute is what keeps track of the official time for the United States and the way they do this is they have a physical measurement laboratory that has an atomic clock and it's called a Cesium Fountain Atomic Clock, this type of clock is accurate to one second for 300 million years.

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_{[FOCS 1, a continuous cold caesium fountain atomic clock -Wikipedia]}

Don't you think it’s pretty cool that these watches or clocks sync automatically without having to do it manually?
That's the cool fact about radio-controlled clocks or watches, they help you do it automatically with super-accurate atomic clocks within minutes without you having to manually set them up.

What are atomic clocks?

Atomic clocks are actually quartz clocks -just like the ones you have at home. The difference is that an ordinary quartz clock relies purely on the oscillations of its quartz crystal to count seconds. As we've already seen, the rate at which quartz vibrates is affected by things like ambient temperature, so although a quartz clock is generally very accurate, it doesn't necessarily keep time as well as you might think. By contrast, an atomic clock has an extra mechanism pulsating atoms that it uses to keep an ordinary quartz clock to time.
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The NIST has a radio station that broadcasts out the exact time every minute, it broadcasts the year, day, hour and the minute as well as whether it's daylight savings time or not at the time. You can also see this time on www.time.gov, it's a little bit of an outdated looking website but it will give you the exact official time.

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_{[Frequency travel distance]}

Another interesting thing about this radio signal is that it's broadcasted at 60 kilohertz, a frequency this low can travel very far, it can actually cover all of the United States and even into other parts of Canada and Mexico.

The NIST has a big radio station with four or five towers that broadcast all across the continent and radio frequencies this low are always reserved for either government or scientific purposes because they are so useful at having long-range communication. It's a lot lower frequency than AM radio which is about 500 kilohertz or more. However, this low frequency does mean it's a very slow data rate, when they send out this time signal, it takes about a full minute to send out the whole signal because it's so slow even though it's so little information.

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_{[NIST radio station -Nist.gov]}

If you do get one of these watch and set it up, it's probably not going to be an instant setting, it might take at least a minute because it's going to miss the first one and then take a full minute to get the next one or it could take even longer if it's a poor signal.

It's estimated that there are more than 50 million devices using this radio signal, anything from wristwatches, wall clocks, clock radios can have a little radio signal and take advantage of that true atomic clock.

Next time you buy a cheap wristwatch on a store and it sets itself and claims it's super-accurate, you can now know how that can be possible.
I hope you guys found this interesting, you can share your thoughts about this by leaving a reply.

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References: 1 - 2 - 3

Image sources: 1 - 2 - 3 - 4 - 5

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