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Time is reverenced to UTC time, which does not vary with timezones, local time is calculated from UTC. The GPS satellites continuously transmit precise time information. GPS time is currently 14 seconds ahead of UTC and is not adjusted for leap seconds. GPS time can easily be adjusted to provide UTC time for computer network time synchronisation. The GPS satellites broadcast a very weak low-power radio signal. The signal has two frequencies, L1 and L2. L1 is intended as a civilian GPS band broadcast at 1575.42 MHz. L2 should provide stronger signal transmissions in the future. The signal travels in a straight line and can pass through clouds, glass and plastics but is blocked by objects such as metal and brickwork. Therefore, ideally, a GPS antenna requires a good view of the sky. The ideal location for a GPS antenna is on rooftop with a good view of the sky. If it is impractical to locate a roof-mounted antenna, installation on the side of a building can be adequate. GPS provides a free-to-air precision time and frequency service. Many computer networks utilise the GPS clock as an accurate timing reference for computer synchronisation. Precise GPS NTP server systems utilise GPS reference clocks as an external synchronisation source. The GPS system can supply highly precise time and frequency information accurate to a couple of nanoseconds. This accuracy is generally more than enough for most computer network timing applications. Most GPS receivers transmit time and positioning information in a serial format using the standard NMEA protocol. Information is transmitted as sentences of character strings. Also, a precise pulse output is generated which indicates the start of each second. This timing pulse can be converted to a RS232 signal level and fed into a RS232 control line interrupt to provide a precise timing reference. When the timing pulse is combined with the NMEA output sentences, a very accurate timing reference becomes available for use by NTP servers or computer timing equipment. Article Source: http://www.articlewheel.com
David Evans is an expert in the field of computer time synchronisation solutions and provides a technical authoring service to the time and frequency industry. Click here to find out more about GPS NTP server solutions.
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