Time Synchronisation

Accurate time using Atomic Clocks is available across North America using the WWVB Atomic Clock time signal transmitted from Fort Collins, Colorado; it provides the ability to synchronize the time on computers and other electrical equipment.

The North American WWVB signal is operated by NIST – the National Institute of Standards and Technology. WWVB has high transmitter power (50,000 watts), a very efficient antenna and an extremely low frequency (60,000 Hz). For comparison, a typical AM radio station broadcasts at a frequency of 1,000,000 Hz. The combination of high power and low frequency gives the radio waves from WWVB a lot of bounce, and this single station can therefore cover the entire continental United States plus much of Canada and Central America.

The time codes are sent from WWVB using one of the simplest systems possible, and at a very low data rate of one bit per second. The 60,000 Hz signal is always transmitted, but every second it is significantly reduced in power for a period of 0.2, 0.5 or 0.8 seconds: • 0.2 seconds of reduced power means a binary zero • 0.5 seconds of reduced power is a binary one. • 0.8 seconds of reduced power is a separator. The time code is sent in BCD (Binary Coded Decimal) and indicates minutes, hours, day of the year and year, along with information about daylight savings time and leap years.

The time is transmitted using 53 bits and 7 separators, and therefore takes 60 seconds to transmit. A clock or watch can contain an extremely small and relatively simple antenna and receiver to decode the information in the signal and set the clock’s time accurately. All that you have to do is set the time zone, and the atomic clock will display the correct time.

Dedicated NTP time servers that are tuned to receive the WWVB time signal are available. These devices connect o a computer network like any other server only these receive the timing signal and distribute it to other machines on the network using NTP (Network Time Protocol).

Atomic clocks are incredibly expensive and generally they are normally only to be found in large scale physics laboratories such as MIT (Massachusetts Institute of Technology), NIST (National Institute of Standards and Technology (Colorado) or the National Physical Laboratory in the UK.

Fortunately many national laboratories broadcast the UTC (Coordinated Universal Time) time from their atomic clocks via a radio transmission.

In the US the national timing broadcast is called WWVB and is broadcast by NIST (National Institute fro Standards and Time) in Fort Collins, Colorado. The WWVB broadcast is used by millions of people throughout North America to synchronize consumer electronic products like wall clocks, clock radios, and wristwatches. In addition, WWVB is used for high-level applications such as network time synchronization utilizing NTP.

The time code contains the year, day of year, hour, minute, second, and flags that indicate the status of Daylight Saving Time, leap years, and leap seconds.

WWVB broadcasts on 2.5, 5, 10, 15, and 20 MHz and for most users in the United States, the received accuracy should be less than 10 milliseconds (1/100 of a second).

While many NTP servers now use GPS to receive a timing reference, the advantage of using a radio transmission is that a signal can be received indoors (a GPS antenna needs a good view of the sky).

However, the radio signal has a finite range and can be blocked by skyscrapers, mountains and dense conurbations. A radio based NTP server usually consists of a rack-mountable time server, and an antenna, consisting of a ferrite bar inside a plastic enclosure, which receives the radio time and frequency broadcast. The antenna should always be mounted horizontally at a right angle toward the transmission for optimum signal strength.

Similar national timing transmissions are broadcast from other countries in the UK the signal is referred to as MSF and is broadcast by the National Physical Laboratory in Cumbria, other systems are broadcast in Frankfurt, Germany (DCF-77), Japan (JJY) and France (TDF)

Atomic clocks are incredibly expensive and generally they are normally only to be found in large scale physics laboratories such as MIT (Massachusetts Institute of Technology), NIST (National Institute of Standards and Technology (Colorado) or the National Physical Laboratory in the UK.

Fortunately many national laboratories broadcast the UTC (Coordinated Universal Time) time from their atomic clocks via a radio broadcast.

In the UK the national timing broadcast is called MSF and is broadcast by NPL (National Physical Laboratory) in Cumbria. The MSF broadcast is used by throughout the UK and parts of Europe to synchronise consumer electronic products like wall clocks, clock radios, and wristwatches. In addition, MSF is used for high-level applications such as network time synchronisation utilising NTP.

The time code contains the year, day of year, hour, minute, second, and flags that indicate the status of Daylight Saving Time, leap years, and leap seconds.

MSF operates on a frequency of 60 kHz and carries a time and date code that can be received and decoded by a wide range of readily available radio-controlled clocks and provides a received accuracy should be less than 10 milliseconds (1/100 of a second).

While many NTP servers now use GPS to receive a timing reference, the advantage of using a radio transmission is that a signal can be received indoors (a GPS antenna needs a good view of the sky).

However, the radio signal has a finite range and can be blocked by skyscrapers, mountains and dense conurbations. A radio based NTP server usually consists of a rack-mountable time server, and an antenna, consisting of a ferrite bar inside a plastic enclosure, which receives the radio time and frequency broadcast. The antenna should always be mounted horizontally at a right angle toward the transmission for optimum signal strength.

Similar national timing transmissions are broadcast from other countries in the US the signal is referred to as WWVB and is broadcast by the NIST (National Institute for Standards and Technology) in Fort Collins, Colorado, other systems are broadcast in Frankfurt, Germany (DCF-77), Japan (JJY) and France (TDF).

This article discusses the development of atomic clocks, why accuracy is so important, how they developed and the next generation of atomic clocks that offer increased accuracy.

Atomic clocks have been with us for over fifty years now and most people have heard of them and know they are very accurate, but how accurate are they and why do we need such accurate clocks?

Atomic clocks are used by many of us even if we are not aware of it. The time they tell is relayed around the world and picked up by time servers using the protocol NTP to synchronise networks, they are vital for lots of technologies, such as global satellite navigation, and TV signal timings.

Before the development of the atomic clock the most precise timekeeping devices were electronic clocks which would lose a second or two every week. These had largely replaced mechanical clocks which were less accurate still.

Mankind has always had a fascination for keeping track of the time but knowing the precise time has never been too important. A second or even a minute’s difference does not affect our day-to-day lives.

However, as technology has advanced the need for more precise timekeeping has increased. Satellites that have to be navigated and communicate with the Earth from hundred, thousands and even millions of miles away require exact timing. Light and therefore radio waves can travel 300,000 km every second so slight inaccuracies in time can have massive differences.

The first accurate atomic clock was built y Britain’s National Physical Laboratory in 1955 by Dr Louis Essen who based his clock around the oscillation of the caesium -133 atom. The idea was actually first conceived as far back as 1879 when Lord Kelvin proposed that time-keeping based on how atoms behaved would be a better way to count time intervals than anything else.

The first generation of atomic clocks (also known as caesium oscillators) used the frequency of this atom which oscillates 9,192,631,770 times every second. Essen’s model was accurate to a second every 300 years but developments of the caesium oscillator mean they can now achieve accuracies of one second every 80 million years.

Yet as technologies get more advanced, scientists strive to make better and more accurate clocks. Rubidium standard clocks offer no better accuracy than caesium models but are smaller and cost less (caesium oscillators are generally only to be found in large-scale physics laboratories).

Clocks using just a single atom have been developed that offer even more accuracy. A clock based on a single mercury atom has achieved accuracies of one second in 400 million years and it is expected that a new type of strontium clock that uses light will go even better.

The future for atomic clocks is ever increasing accuracy combined with scaling down the size and cost of them. The American National Institute of Standards and Technology (NIST) have unveiled a chip-sized atomic clock that boasts millisecond accuracy.

Atomic clocks are now part and parcel of our lives without the time signals they transmit to the world that are picked up by NTP servers modern communication from Internet shopping and GPS and technological advances such as satellite navigation would become impossible.