Category: atomic clocks

Types of Atomic Clock Receivers

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MSF atomic clock receiver

The controlling radio signal for the National Physical Laboratory‘s atomic clock is transmitted on the MSF 60kHz signal via the transmitter at , CumbriaAnthorn, operated by British Telecom. This radio atomic clock time signal should have a range of some 1,500 km or 937.5 miles. All of the British Isles are of course within this radius.
The National Physical Laboratory’s role as keeper of the national time standards is to ensure that the UK time-scale agrees with Co-ordinated Universal Time (UTC) to the highest levels of accuracy and to make that time available across the UK. As an example, the MSF (MSF being the three-letter call sign to identify the source of the signal) radio broadcast provides the time signal for, electronic share trading, the clocks at most railway stations and for BT’s speaking clock.

DCF atomic clock receiver

The controlling radio signal for the German clock is transmitted via long wave from the DCF 77kHz transmitter at Mainflinger, near Dieburg, some 25 km south east of Frankfurt – the transmitter of German National Time Standards. It is similar in operation to the Cumbria transmitter, however there are two antennas (radio masts) so the radio atomic clock time signal can be maintained at all times.

Long wave is the preferred radio frequency for transmitting radio atomic clock time code binary signals as it performs most consistently in the stable lower part of the ionosphere. This is because the long wave signal carrying the time code to your timepiece travels in two ways; directly and indirectly. Between 700 km (437.5 miles) to 900 km (562.5 miles) of each transmitter the carrier wave can travel directly to the timepiece. The radio signal also reaches the timepiece via being bounced off the underside of the ionosphere. During the hours of daylight a part of the ionosphere called the “D layer” at an altitude of some 70 km (43.75 miles) is responsible for reflecting the long wave radio signal. During the hours of darkness when the sun’s radiation is not acting from outside the atmosphere, this layer rises to an altitude of some 90 km (56.25 miles) becoming the “E layer” in the process. Simple trigonometry will show that signals thus reflected will travel further.

A large part of the European Union area is covered by this transmitter facilitating reception for those who travel widely in Europe. The German clock is set on Central European Time – one hour ahead of U.K. time, following an inter-governmental decision, from the 22nd October, 1995, U.K. time will always be 1 hour less than European Time with both the U.K. and mainland Europe advancing and retarding clocks at the same “time”.

WVVB atomic clock receiver

A radio atomic clock system is available in North America set up and operated by NIST – the National Institute of Standards and Technology, located in Fort Collins, Colorado.

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 MSF a lot of bounce, and this single station can therefore cover the entire continental United States plus much of Canada and Central America.

The radio atomic clock 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 radio atomic clock antenna and receiver to decode the information in the signal and set the atomic clock time accurately. All that you have to do is set the time zone, and the atomic clock will display the correct time.

Finding the Time

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Finding out what the time is, is something we all take for granted. Clocks are everywhere and a glance at a wristwatch, clock tower, computer screen or even a microwave will tell us what the time is. However, telling the time has not always been that easy.

Clocks didn’t arrive until the middle ages and their accuracy was incredibly poor. True time telling accuracy didn’t arrive until after the arrival of the electronic clock in the nineteenth century. However, many of the modern technologies and applications that we take for granted in the modern world such as satellite navigation, air traffic control and internet trading require a precision and accuracy that far exceeds an electronic clock.

Atomic clocks are by far the most accurate time telling devices. They are so accurate that the world’s global timescale that is based on them (Coordinated Universal Time) has to be occasionally adjusted to account for the slowing of the Earth’s rotation. These adjustments take the form of additional seconds known as leap seconds.

Atomic clock accuracy is so precise that not even a second of time is lost in over a million years whilst an electronic clock by comparison will lose a second in a week.

But is this accuracy really necessary? When you look at technologies such as global positioning then the answer is yes. Satellite navigation systems like GPS work by triangulating time signals generated by atomic clocks onboard the satellites. As these signals are transmitted at the speed of light they travel nearly 100,000 k m each second. Any inaccuracy in the clock by even a thousandth of a second could see the positioning information out by miles.

Computer networks that have to communicate with each other across the globe have to ensure they are running not just accurate time but also are synchronised with each other. Any transactions conducted on networks without synchronisation can result in all sorts of errors.

Fort his reason computer networks use NTP (Network Time Protocol) and network time servers often referred to as an NTP server. These devices receive a timing signal from an atomic clock and distribute it amongst a network in doing so a network is ensured to be as accurate and precise as possible.

Difficulties in telling the time!

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Precision in telling the time has never been as important as it is now. Ultra precise atomic clocks are the foundation for many of the technologies and innovations of the twentieth century. The internet, satellite navigation, air traffic control and global banking all just a few of the applications that is reliant on particularly accurate timekeeping.

The problem we have faced in the modern age is that our understanding exactly of what time is has changed tremendously over the last century. Previously it was thought that time was constant, unchanging and that we travelled forward in time at the same rate.

Measuring the passing of time was straight forward too. Each day, governed by the revolution of the Earth was divided into 24 equal amounts – the hour.  However, after the discoveries of Einstein during the last century, it was soon discovered time was not at all constant and could vary for different observers as speed and even gravity can slow it down.

As our timekeeping became more precise another problem became apparent and that was the age old method of keeping track of the time, by using the Earth’s rotation, was not an accurate method.

Because of the Moon’s gravitational influence on our oceans, the Earth’s spin is sporadic, sometimes falling short of the 24 hour day and sometimes running longer.

Atomic clocks were developed to try to keep time as precise as possible. They work by using the unchanging oscillations of an atom’s electron as they change orbit. This ‘ticking’ of an atom occurs over nine billion times a second in caesium atoms which makes them an ideal basis for a clock.

This ultra precise atomic clock time (known officially as International Atomic Time – TAI) is the basis for the world’s official timescale, although because of the need to keep the timescale in parallel with the rotation of the Earth (important when dealing with extra terrestrial bodies such as astronomical objects or even satellites) addition seconds, known as leap second, are added to TAI, this altered timescale is known as UTC – Coordinated Universal Time.

UTC is the timescale used by businesses, industry and governments all around the world. As it is governed by atomic clocks it means the entire world can communicate using the same timescale, governed by the ultra-precise atomic clocks. Computer networks all over the world receive this time using NTP servers (Network Time Protocol) ensuring that everybody has the same time to within a few milliseconds.

Synchronising Computer Networks to an Atomic Clock

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Atomic clocks are well-known for being accurate. Most people may never have seen one but are probably aware that atomic clocks keep highly precise time. In fact modern atomic clock will keep accurate time and not lose a second in one hundred million years.

This amount of precision may seem overkill but a multitude of modern technologies rely on atomic clocks and require such a high level of precision. A perfect example is the satellite navigation systems now found in most auto cars. GPS is reliant on atomic clocks because the satellite signals used in triangulation travel at the speed of light which in a single second can cover nearly 100,000 km.

So it can be seen how some modern technologies rely on this ultra precise timekeeping from atomic clocks but their use doesn’t stop there. Atomic clocks govern the world’s global timescale UTC (Coordinated Universal Time) and they can also be used to synchronise computer networks too.

It may seem extreme to use this nanosecond precision to synchronise computer networks too but as many time sensitive transactions are conducted across the internet with such trades as the stock exchange where prices can fall or rise each and every second it can be seen why atomic clocks are used.

To receive the time from an atomic clock a dedicated NTP server is the most secure and accurate method. These devices receive a time signal broadcast by either atomic clocks from national physics laboratories or direct from the atomic clocks onboard GPS satellites.

By using a dedicated NTP server a computer network will be more secure and as it is synchronised to UTC (the global timescale) it will in effect be synchronised with every other computer network using a NTP server.

The World in Synchronisation

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Time synchronisation plays an ever more important role in the modern world with more and more technologies reliant on accurate and reliable time.

Time synchronisation is not just important but can also be crucial in the safe running of systems such as air traffic control that simply couldn’t function without accurate synchronisation. Think of the catastrophes that could happen in the air of aircraft were out of synchronisation with each other?

In global commerce too accurate and reliable time synchronisation is highly important. When the world’s stock markets open in the morning and traders from across the world buy stock on their computers. As stock fluctuates second by second if machines are out of synchronisation it could cost millions.

But synchronisation is also imperative in modern computer networking; it keeps systems secure and enables proper control and debugging of systems. Even if a computer network is not involved in any time sensitive transactions a lack of synchronisation can leave it vulnerable to malicious attacks and can also be susceptible to data loss.

Accurate synchronisation is possible in computer networking thanks to two developments: UTC and NTP.

UTC is a timescale -coordinated universal time, it is based on GMT but is controlled by an array of atomic clocks making it accurate to within a few nanoseconds.

NTP is a software protocol – Network Time Protocol, designed to accurately synchronise computer networks to a single time source. Both of these implementations come together in a single device which is relied upon the world over to synchronise computer networks – the NTP server.

An NTP time server or network time server is a device that receives the time from an atomic clock, UTC source and distributes it across a network. Because the time source is continually checked by the time server and is from an atomic clock it makes the network accurate to within a few milliseconds of UTC providing synchronisation on a global scale.

The Clocks to Spring Forward at the Weekend

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It’s that time of year again when we lose an hour over the weekend as the clocks go forward to British Summer Time. Twice a year we alter the clocks but in an age of UTC (Coordinated Universal Time) and time server synchronisation is it really necessary?

The changing of the clocks is something that was discussed just before World War I when London builder William Willet suggested the idea as a way of improving the nation’s health (although his initial idea was to advance the clocks twenty minutes on each Sunday in April).

His idea wasn’t taken up although it sowed the seed of an idea and when the First World War erupted it was adopted by many nations as a way to economise and maximise daylight although many of these nations discarded the concept after the war, several including the UK and USA kept it.

Daylight saving has altered over the years but since 1972 it has remained as British Summer Time (BST) in the summer and Greenwich Meantime in the winter (GMT). However, despite is use for nearly a century the changing of the clocks remains controversial. For four years Britain experimented without daylight changing but it was proved unpopular in Scotland and the North where the mornings were darker.

This timescale hopping does cause confusion (I for one will miss that hour extra in bed on Sunday) but as the world of commerce adopts the global civil timescale (which fortunately is the same as GMT as UTC is adjusted with leap seconds to ensure GMT is unaffected by the slowing of the Earth’s rotation) is it still necessary?

The world of time synchronisation certainly doesn’t need to adjust for daylight saving. UTC is the same the world over and thanks to devices such as the NTP server can be synchronised so the entire world runs the same time.

NTP Synchronization and FAQ

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With a variety of acronyms and timescales the world of time synchronisation can be quite confusing here are some frequently asked questions we hope will help enlighten you.

What is NTP?

NTP is a protocol designed to synchronize computer networks across the internet or LAN (Local Area Networks). It is not the only time synchronization protocol available but it is the most widely used and the oldest having been conceived in the late 1980’s.

What are UTC and GMT?

UTC or Coordinated Universal Time is a global timescale, it is controlled by highly accurate atomic clocks but kept the same as GMT (Greenwich Meantime) by the use of leap seconds, added when the Earth’s rotation slows down. Strictly speaking GMT is the old civil timescale and based on when the sun is above the meridian line, however, as the two systems are identical in time thanks to leap seconds, UTC is often referred to as GMT and vice versa.

And a NTP Time Server?

These are devices that synchronize a computer network to UTC by receiving a time signal and distributing it with the protocol NTP which ensures all devices are running accurately to the timing reference.

Where to get UTC time from?

There are two secure methods of receiving UTC. The first is to utilize the long wave time signals broadcast by NIST (WWVB) NPL in the UK (MSF) and the German NPL (DCF) The other method is to use a the GPS network. GPS satellites broadcast an atomic clock signal that can be utilised and converted to UTC by the GPS NTP server.

NTP GPS Server Using Satellite Time Signals

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The NTP GPS server is a dedicated device that uses the time signal from the GPS (Global Positioning System) network. GPS is now a common tool for motorists with satellite navigation devices fitted to most new cars. But GPS is far more than just an aid for positioning, at the very heart of the GPS network is the atomic clocks that are inside each GPS satellite.

The GPS system works by transmitting the time from these clocks along with the position and velocity of the satellite. A satellite navigation receiver will work out when it receives this time how long it took to arrive and therefore how far the signal travelled. Using three or more of these signals the satellite navigation device can work out exactly where it is.

GPS can only do this because of the atomic clocks that it uses to transmit the time signals. These time signals travel, like all radio signals, at the speed of light so an inaccuracy of just 1 millisecond (1/1000 of a second) could result in the satellite navigation being nearly 300 kilometres out.

Because these clocks have to be so accurate, they make an ideal source of time for a NTP time server. NTP (Network Time Protocol) is the software that distributes the time from the time server to the network. GPS time and UTC (Coordinated Universal Time) the civil timescale is not quite the same thing but are base don the same timescale so NTP has no trouble converting it. Using a dedicated NTP GPS server a network can be realistically synchronised to within a few milliseconds of UTC

The GPS clock is another term often given to a GPS time server. The GPS network consists of 21 active satellites (and a few spare) 10,000 miles in orbit above the Earth and each satellite circles the Earth twice a day. Designed for satellite navigation, A GPS receiver needs at least three satellites to maintain a position. However, in the case of a GPS clock just one satellite is required making it far easier to obtain a reliable signal.

Each satellite continuously transmits its own position and a time code. The time code is generated by an onboard atomic clock and is highly accurate, it has to be as this information is used by the GPS receiver to triangulate a position and if it was just half a second out the Sat Nav  unit would be inaccurate by thousands of miles.

The Importance of the Atomic Clock

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Most people have vaguely heard of the atomic clock and presume they know what one is but very few people know just how important atomic clocks are for the running of our day to day lives in the twenty first century.

There are so many technologies that are reliant on atomic clocks and without many of the tasks we take for granted would be impossible. Air traffic control, satellite navigation and internet trading are just a few of the applications that are reliant on the ultra precise chronometry of an atomic clock.

Exactly what an atomic clock is, is often misunderstood. In simple terms an atomic clock is a device that uses the oscillations of atoms at different energy states to count ticks between seconds. Currently caesium is the preferred atom because it has over 9 billion ticks every second and because these oscillations never change it makes them a highly accurate method of keeping time.

Atomic clocks despite what many people claim are only ever found in large scale physics laboratories such as NPL (UK National Physical Laboratory) and NIST (US National Institute of Standards and Time). Often people suggest they have an atomic clock that controls their computer network or that they have an atomic clock on their wall. This is not true and what people are referring to is that they have a clock or time server that receives the time from an atomic clock.

Devices like the NTP time server often receive atomic clock signals form places such as NIST or NPL via long wave radio. Another method for receiving time from atomic clocks is using the GPS network (Global Positioning System).

The GPS network and satellite navigation are in fact a good example of why atomic clock synchonization is much needed with such high level of accuracy. Modern atomic clocks such as those found at NIST, NPL and inside orbiting GPS satellites are accurate to within a second every 100 million years or so. This accuracy is crucial when you examine how something like a cars GPS satellite navigation system works.

A GPS system works by triangulating the time signals sent from three or more separate GPS satellites and their onboard atomic clocks. Because these signals travel at the speed of light (nearly 100,000km a second) an inaccuracy of even one whole millisecond could put the navigational information out by 100 kilometres.

This high level of accuracy is also required for technologies such as air traffic control ensuring our crowded skies remain safe and is even critical for many Internet transactions such as trading in derivatives where the value can rise and fall every second.

Step by Step Installing A Dedicated NTP Time Server

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A time server is a crucial piece of kit for any network. Time synchronisation is imperative in keeping a network secure and reliable. Time synchronisation, however, need not be the headache many administrators assume it is going to be.

Most of the difficulties of time synchronisation have been taken care of thanks to the protocol NTP (Network Time Protocol). Whilst NTP is not the only time synchronisation software available it is by far the most widely used (due mainly to the fact that it has been around since the 1980’s and is still being developed today).

NTP uses a single time source and distributes it from machine-to-machine checking each PC or device for drift then adjusting for it. NTP is normally installed on Windows and Linux systems (or at least a simplified version called SNTP) although it is freely downloadable from the NTP homepage. While NTP can quite easily receive any time source from the Internet this can cause major security issues no to mention a lack of accuracy that many online NTP servers suffer from.

The most accurate and secure method is to use an external network time server as these sit within the firewall. They also receive a UTC (Coordinated Universal Time) reference direct from an atomic clock which makes them stratum 1 devices. Most internet time servers are stratum 2 servers. NTP uses strata to define how far away a server is from the source so an atomic clock is a stratum 0 device while a computer that receives time direct from a NTP server becomes a stratum 2 device and so on.

The only decision that really needs to be made when installing a dedicated NTP time server is which time reference is best. There are two main methods of receiving a secure, accurate and authenticated UTC time reference; the GPS network (Global Positioning System) or national physics laboratories long wave radio transmissions.

The latter system is not available in every country although the USA, UK and Germany have strong signals known as WWVB, MSF and DCF respectively. These can often be picked up outside the borders of these countries although the signals are vulnerable to interference, outages and local topography.

A GPS NTP server system is less vulnerable to these things and as long as there is a clear view of the sky (such as a rooftop or open window) the GPS time signal can be picked up anywhere on the globe.