Category: GPS

Choosing a dedicated GPS Time Server

  |   By

Because of the advancement in satellite navigation technologies and the increased coverage of the American GPS satellite network, many more administrators are choosing GPS as a source for a timing reference to synchronize their time servers too.

Traditionally many more people opted to receive a timing source from either across the Internet or via specialist national time and frequency transmissions.  However, the Global Positioning System is now by far the most popular method to receive a UTC time source from.

UTC (Coordinated Universal Time) is the global timescale based on the time told by atomic clocks which are the most accurate of time keeping devices.

A GPS time server is a relatively simple piece of hardware. Normally it consists of a dedicated NTP server with software, a GPS receiver and a GPS antenna. The antenna is the only drawback in using a dedicated GPS time server as it has to be positioned on the roof to have a clear view of the sky, although some dedicated GPS time servers can still keep time synchronized if they only receive a signal for a few hours a day, although this is not the most accurate way of time synchronization.

Once connected, the GPS time server will receive the time signal from the GPS satellites and then distribute it to all devices that require synchronization.

Most time servers, whether they receive a GPS signal or not, will use Network Time Protocol (NTP) to distribute the time signal to all devices.

NTP is one of the Internet’s oldest protocols and is by far the most widespread time synchronization protocols used. NTP is under constant development and can accurately synchronise a network to within a few milliseconds of UTC time via a dedicated GPS time server.

Use of GPS for Computer Timing Applications

  |   By

The Global Positioning System (GPS) is now a familiar tool in helping motorists to navigate but GPS has more uses than merely triangulating a position for direction finding, it can be utilized to provide time and frequency information worldwide.

Developed by the United States military, GPS incorporates at least 24 communication satellites in high orbit, all of which contain precise timing equipment to enable the satellite to triangulate positions with accuracy.

However, each satellite’s highly accurate atomic clock timing reference can also be used by NTP (Network Time Protocol) servers to synchronise computer networks using the highly accurate GPS time signal as an external reference.

GPS is an ideal time and frequency source because it can provide highly accurate time anywhere in the world using relatively cheap components. Each GPS satellite transmits in two frequencies L2 for the military use and L1 for use by civilians transmitted at 1575 MHz, Low-cost GPS antennas and receivers are now widely available.

The radio signal transmitted by the satellite can pass through windows but can be blocked by buildings so the ideal location for a GPS antenna is on a rooftop with a good view of the sky. The more satellites it can receive from the better the signal. However, roof-mounted antennas can be prone to lighting strikes or other voltage surges so a suppressor is recommend; installed inline on the GPS cable.

The cable between the GPS antenna and receiver is also critical. The maximum distance that a cable can run is normally only 20-30 metres but a high quality coax cable combined with a GPS amplifier placed in-line to boost the gain of the antenna can allow in excess of 100 metre cable runs.

A GPS receiver then decodes the signal sent from the antenna to a computer readable protocol which can be utilised by most time servers and operating systems including, Windows, LINUX and UNIX.

The GPS receiver also outputs a precise pulse every second that GPS NTP servers and computer time servers may utilise to provide ultra-precise timing. The pulse-per-second timing on most receivers is accurate to within 0.001 of a second of UTC (Coordinated Universal Time)

GPS is ideal in providing NTP time servers or stand-alone computers with a highly accurate external reference for synchronisation.

Even with relatively low cost equipment, accuracy of a hundred nanoseconds (a nanosecond = a billionth of a second) can be reasonably achieved using GPS as an external reference.