WWVB

NIST Time & Frequency Service (callsign WWVB) is a longwave time signal radio station near Fort Collins, Colorado, and is operated by the United States Government via theNational Institute of Standards and Technology (NIST). Most radio-controlled clocks in North America use WWVB's transmissions to set the correct time. The normal signal transmitted from WWVB is 70 kW ERP and uses a 60 kHz carrier wave yielding a frequency uncertainty of less than 1 part in 1012. The time code signal is derived from a set of atomic clocks located at the site, and transmitted using the IRIG "H" format and modulated onto the carrier wave using pulse-width modulation and amplitude-shift keying at one bit per second. A single complete frame of time code begins at the start of each minute, lasts one minute, and conveys the year, day of year, hour, minute, and other information as of the beginning of the minute. WWVB is co-located with WWV, a time signal station that broadcasts in both voice and time code on multiple shortwave radio frequencies. WWVB is not an acronym or abbreviation but a call sign for the radio station. While most time signals encode the local time of the broadcasting nation, the United States spans multiple time zones, so WWVB broadcasts the time in Coordinated Universal Time (UTC). Radio-controlled clocks can then apply time zone and daylight saving time offsets as needed to display local time. The time used in the broadcast is set by the NIST Time Scale, known as UTC(NIST). This time scale is the calculated average time of an ensemble of master clocks, themselves calibrated by the NIST-F1 and NIST-F2 cesium fountain atomic clocks. In 2011, NIST estimated the number of radio clocks and wristwatches equipped with a WWVB receiver at over 50 million.