Atomic Clocks and the GPS Time Server

Atomic clocks have been around since the 1950’s when NPL (National Physical Laboratory) in the UK developed the first reliable caesium based clock. Before atomic clocks, electronic clocks were the most accurate method of keeping track of time but while an electrical clock may lose a second in every week or so, a modern atomic clock will not lose a single second in hundreds of millions of years.

Atomic clocks are not just used to keep track of time. The atomic clock is an integral part of the GPS system (Global Positioning System) as each GPS satellite has its own onboard atomic clock that generates a time signal that is picked up by GPS receivers who can calculate their position by using the precise signal from three or more satellites.

Atomic clocks need to be used as the signal s from the satellites travel at the speed of light and as light travels nearly 300,000 km each second any slight inaccuracy could put navigation out by miles.

A GPS time server is a network time server that uses the time signal from the GPS network’s satellites to synchronise the time on computer networks. A GPS time server often uses NTP (Network Time Protocol) as a method of distributing time which is why these devices are often referred to as NTP GPS time servers.

Computer networks that are synchronised using a dedicated time server are normally synchronised to UTC (Coordinated Universal Time) and while the GPS signal is not UTC, GPS time, like UTC, is based on International Atomic Time (TAI) and is easily converted by NTP.

How a GPS Time Server Works

A GPS time server is really a communication device. Its purpose is to receive a timing signal and then distribute it amongst all devices on a network. Time server s are often called different things from network time server, GPS time server, radio time server and NTP server.

Most time servers use the protocol NTP (Network Time Protocol). NTP is one of the Internet’s oldest protocols and is used by the majority of machines that use a time server. NTP is often installed, in a basic form, in most operating systems.

A GPS time server, as the names suggests, receives a timing signal from the GPS network. GPS satellites are really nothing more than orbiting clocks. Onboard each GPS satellite is an atomic clock. The ultra-precise time from this clock is what is transmitted from the satellite (along with the satellite’s position).

A satellite navigation system works by receiving the time signal from three or more satellites and by working out the position of the satellites and how long the signals took to arrive, it can triangulate a position.

A GPS time server needs even less information and only one satellite is required in order to receive a timing reference. A GPS time server’s antenna will receive a timing signal from one of the 33 orbiting satellites via line of sight, so the best place to fix the antenna is the roof.

Most dedicated GPS NTP time servers require a good 48 hours to locate and get a steady fix on a satellite but once they have it is rare for communication to be lost.

The time relayed by GPS satellites is known as GPS time and although it differs to the official global timescale UTC (Coordinated Universal Time) as they are both based on atomic time (TAI) GPS time is easily converted by NTP.

A GPS time server is often referred to as a stratum 1 NTP device, a stratum 2 device is a machine that receives the time from the GPS time server. Stratum 2 and stratum 3 devices can also be used as a time servers and in this way a single GPS time server can operate as a timing source for an unlimited amount of computers and devices as long as the hierarchy of NTP is followed.

GPS Time Server – Keeping Time with GPS

The Global Positioning System along with the Internet has changed the way we live our lives. Thousands of motorists use them daily to navigate their around the country’s roads while airline pilots and ship’s captains use them for the same purpose on our seas and in our skies.

But GPS has more uses than just navigation as the technology that GPS utilises is based around the atomic clock. Atomic clocks are highly accurate devices, so accurate that within a billion years they will not lose a second in time.

It is this accuracy that allows satellite navigation devices to triangulate the positioning by measuring the time it takes for the GPS signals to arrive. As radio waves, such as those broadcast by the GPS satellites travel at the speed of light, an inaccuracy of just one second could see the positioning device inaccurate by 300,000 km (the speed light travels per second).

This timing signal broadcast by the satellites can also be utilised by a GPS time server. GPS time servers use the atomic clock signal and convert it into UTC (Coordinated Universal Time) which can be used by network time servers.

These time servers are often referred to as a GPS time server as they use GPS as a timing source to synchronise entire computer networks to.  GPS signals are highly accurate and available anywhere on the planet.

Receiving UTC

A simple source of UTC (Coordinated Universal Time) is the Global Positioning System. GPS offers reliable, worldwide coverage and the potential for extremely accurate timing via a GPS time server.
When you use a GPS time server to receive, be sure to let it obtain a good satellite lock so it can update correctly.

This is the main cause for GPS time servers to display the incorrect time. To test the accuracy of a GPS time server, you should verify the accuracy of your GPS’ displayed UTC by comparing it against an accurate time standard such as the MSF signal or by using a guaranteed source of UTC from across the Internet – details of which are posted on the NTP pool.

Reliable, precision timing is available from the Global Positioning System by using a GPS time server as they use the GPS 1PPS signal. Such units provide the current UTC to an accuracy of 1/1000 of a second or better.