The WWVB Time Signal
The WWVB time signal is a dedicated radio broadcast providing an accurate and reliable source of United States civil time, based on the global time scale UTC (Coordinated Universal Time), the WWVB signal is broadcast and maintained by the United States’ NIST laboratory (National Institute for Standards and Time).
The WWVB time signal can be utilised by anyone requiring accurate timing information although its main use is as a source of UTC time for administrators synchronising a computer network with a radio clock. Radio clocks are really another term for a network time server that utilises a radio transmission as a timing source.
Most radio based network time servers use NTP (Network Time Protocol) to distribute the timing information throughout the network.
The WWVB signal is broadcast from Fort Collins, Colorado. It is available 24 hours a day across most of the USA and Canada, although the signal is vulnerable to interference and local topography. Users of the WWVB service receive predominantly a ‘ground wave’ signal. However, there is also a residual ‘sky wave’ which is reflected off the ionosphere and is much stronger at night; this can result in a total received signal that is either stronger or weaker.
The WWVB signal is carried on a frequency of 60 kHz (to within 2 parts in 1012) and is controlled by a caesium atomic clock based at NIST
The signal’s field strength exceeds 100 µV/m (microvolts a meter) at a distance of 1000 km from Colorado – covering much of the USA.
The WWVB signal is in the form of a simple binary code containing time and date information The WWVB time and date code includes the following information: year, month, day of month, day of week, hour, minute, Summer Time (in effect or imminent).
