WWV is the callsign of NIST's shortwave radio station located in Fort Collins, Colorado. WWV's main function is the continuous dissemination of official U.S. Government time signals. The station broadcasts simultaneously on five distinct frequencies: 2.5 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz. These carrier frequencies, as well as the time signals, are derived from a set of atomic clocks located at the transmitter site, which themselves are traceable to NIST's primary frequency standard in Boulder, Colorado using such techniques as GPS common-view observations. WWV is partnered with radio station WWVH, located in Hawaii. Onsite with WWV in Fort Collins, Colorado is also radio station WWVB, which operates on the low frequency of 60 kHz.

WWV is the oldest continuously-operating radio station in the United States, first going on the air in May of 1920, approximately six months before the launch of KDKA. The station was formerly located in Greenbelt, Maryland, on land which now is part of NASA's Goddard Space Flight Center. WWV moved to its present location at Fort Collins on December 1, 1966, allowing better reception of its signal throughout the continental United States.

Broadcast format

WWV transmits the exact time-of-day in two ways at the same time. The first method is through voice announcements made every minute, each followed by a long beep that serves as the "on-time marker" for each announcement. These long beeps are also used to mark off standard intervals of one minute, and are usually tones of 1000Hz.ogg, except for the top of the hour, when a 1500Hz.ogg tone is used. The second method of transmitting the time-of-day is through a continuously-transmitted sub-audible digital time code, which also carries extra information such as whether or not Daylight Saving Time is in effect, and when the next leap second will occur. The voice announcements (made in a male voice to distinguish from WWVH in Hawaii) are useful for people manually setting clocks, while the digital time codes can be used by radio-controlled clocks. The transmitted time is given in Coordinated Universal Time (UTC). WWV also "ticks" each second (except at 29 and 59 seconds past the minute, the omissions used to encode the standard interval of thirty seconds), to allow for accurate manual synchronization. Between seconds one and sixteen inclusive past the minute, the current difference between UTC and UT1 is transmitted by doubling some of the once-per-second ticks. The absolute value of this difference, in tenths of a second, is determined by the number of doubled ticks. If the doubled ticks are between seconds one and eight inclusive past the minute, UT1 is ahead of UTC. If the doubled ticks fall between seconds nine and sixteen inclusive, UT1 is behind UTC.

In most minutes of the hour, WWV transmits standard audio frequencies of 500Hz.ogg and 600Hz.ogg, switching between the two frequencies each minute. These two frequencies are used to synchronize 50 Hz and 60 Hz electrical power supplies respectively. WWV also transmits a 440Hz.ogg tone (a pitch commonly used in music for the note A above middle C) every hour at two minutes past, except for the first hour of the UTC day. Since the 440 Hz tone is only transmitted once per hour, many chart recorders may use this tone to mark off each hour of the day, and likewise, the omission of the 440 Hz tone once per day can be used to mark off each twenty-four hour period.

WWV's broadcasts are not limited to time-of-day and standard time intervals. At 8, 9 and 10 minutes past the hour, WWV stops transmitting its standard audio frequencies to broadcast regular high-seas weather warnings. At 14 and 15 minutes past the hour, reports relating to the health of the U.S. Department of Defense's GPS service are transmitted. And at 18 minutes past the hour, a special "geophysical alert" report is transmitted, containing information on solar activity and shortwave radio propagation conditions. No audio tones are transmitted from WWV between 43 and 51 minutes inclusive past the hour.

External links

• NIST: Time and frequency division