Network Time References: What's Best? Gps Or Radio

The Network Time Protocol is a standard means of disseminating accurate time around the Internet and other computer networks. Accurate time stamps are passed from a time server to clients for synchronisation. A stratum 1 NTP server is a device that obtains precise time from an external reference clock and provides networks with a NTP resource for synchronisation purposes. This article attempts to describe simply the advantages and disadvantages of various GPS and radio time references and how they can be utilised for computer timing.

There are a quite number of radio time and frequency transmissions that are available in various regional locations. In Europe, the DCF-77 radio time and frequency broadcast, based in Germany, serves much of the Central and Northern continent. The UK's MSF transmission serves the UK and much of North-Western Europe. While the WWVB signal is broadcast across the US. Each of these radio broadcasts provides an accurate source of timing information within the regions they serve.

Radio time signals can generally be received by antennas located indoors, lowering installation costs. However, signals can be affected by local topography - such as hills and valleys. There is no guarantee of radio signal reception even well inside the transmission range of the signal. The MSF radio signal broadcast in the UK by the National Physics Laboratory recently moved from Rugby in the East Midlands to Anthorn in Cumbria. Since the move, it has been widely acknowledged that signal reception in the South of England has suffered - even though it is well within the physical reception range for the signal.

The local environment, where the radio antenna is located, can also affect signal reception. Antennas placed inside metal structures can experience poor signal reception. These structures can act as Faraday cages, blocking signal reception. Additionally, antennas located underground may fail to receive an adequate signal.

GPS time references utilise the Global Positioning System intended for worldwide navigation. The GPS system is a constellation of 24 orbiting satellites each broadcasting continuous time and positioning information. Each GPS satellite has an integrated, highly precise, synchronised atomic clock. Timing information can be received anywhere on the face of the planet, providing an antenna can be provided with line of sight to the orbiting satellites.

GPS time references have a number of advantages over their radio-based time and frequency counterparts. Firstly, GPS can be received anywhere in the world and is not restricted by transmitter power and radio signal range. Secondly, the GPS signal is a much more accurate reference than radio solutions, accurate to within nanoseconds rather than milliseconds. Thirdly, GPS timing information can be received by anyone who can provide an antenna with a good view of the sky. GPS antennas do need to have a line of sight view of GPS satellites. The ideal location for a GPS antenna is on a rooftop with a full 360-degree view of the sky. Additionally, if buildings or trees obscure the horizon in anyway, it can affect reception integrity. Roof-mounted antennas can significantly add to the installation costs of a NTP server system.

To summarise, radio and GPS based time and frequency references for network time references both have certain advantages and disadvantages. However, the accuracy of GPS and the guaranteed reception, albeit with roof-mounted antennas, make it the reference of choice for NTP server systems.

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About the Author:
This article was written by David Evans, a technical author in the field of computer time synchronisation technology. Click here, to visit our website for more articles and information on NTP Server solutions.