GPS comes to rescue

The global positioning system was one of the greatest technology breakthroughs of the past century. While early GPS systems were often difficult to use, today's GPS engineers have found new ways to interpret satellite information in way that is user-friendly. One of the challenges for engineers has been how to apply information to the system.

Utilizing satellites in NTP Servers

GPS NTP Server is a dedicated device that uses the time signal from GPS network. GPS is now a common tool for car drivers 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 are atomic clocks that are inside each GPS satellite.

Accurate time from satellites

The GPS system works by transmitting 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 and what time it is.

Atomic Clocks

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.

Atomic Clock

An atomic clock is a type of clock that uses an atomic resonance frequency standard as its timekeeping element.

They are the most accurate time and frequency standards known, and are used as primary standards for international time distribution services, to control the frequency of television broadcasts, and in global navigation satellite systems such as GPS.

PPS Pulse distribution

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

PPS Pulse signal

PPS signals are used for precise timekeeping and time measurement. One increasingly common use is in computer timekeeping, including the NTP protocol. Because GPS is considered a stratum-0 source, a common use for the PPS signal is to connect it to a PC using a low-latency, low-jitter wire connection and allow a program to synchronize to it: this makes the PC a stratum-1 time source.

Note that because the PPS signal does not specify the time, but merely the start of a second, one must combine the PPS functionality with another time source that provides the full date and time in order to ascertain the time both accurately and precisely.

NtpServer with a GPS receiver

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.

Time code and position triangulation

On the other hand a dedicated NTP GPS server receives its time signal from the GPS satellite system (each satellite contains an atomic clock). These signals offer excellent accuracy and furthermore are available everywhere on the planet where there is a clear view of the sky.

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.