WWV is a shortwave ("high frequency" or HF) radio station, located near Fort Collins, Colorado. It has broadcast a continuous time signal since 1945, and implements United States government frequency standards, with transmitters operating on 2.5, 5, 10, 15, and 20 MHz. WWV is operated by the U.S. National Institute of Standards and Technology (NIST), under the oversight of its Time and Frequency Division, which is part of NIST's Physical Measurement Laboratory based in Gaithersburg, Maryland.
WWV was established in 1919 by the Bureau of Standards in Washington, D.C., making it one of the oldest continuously-operating radio stations in the United States. NIST celebrated WWV's centennial on October 1, 2019.
In 1931, the station relocated to the first of three suburban Maryland sites, before moving to a location near Fort Collins in 1966. WWV shares this site with longwave (also known as "low frequency" or LF) station WWVB, which transmits carrier and time code (no voice) at 60 kHz. NIST also operates shortwave station WWVH on Kauai, Hawaii. Both WWV and WWVH announce the time of day each minute in Coordinated Universal Time, and make other recorded announcements of general interest on an hourly schedule, including the Global Positioning System (GPS) satellite constellation status. Because they simultaneously transmit on the same frequencies, WWV uses a male voice in order to differentiate itself from WWVH, which uses a female voice.
Service
Since 1945, WWV has disseminated "official U.S. time" provided by government entities NIST and the United States Naval Observatory (USNO), to ensure that uniform time is maintained throughout the United States and around the world. WWV provides a public service by making time information freely available at all hours.
The time signals generated by WWV allow time-keeping devices such as radio-controlled clocks and wristwatches to automatically maintain accurate time without the need for manual adjustment. These time signals are used by commercial and institutional interests where accurate time plays a vital role in daily operations including shipping, transport, technology, research, education, military, public safety and telecommunications. It is of particular importance in broadcasting, whether it be commercial, public, or private interests such as amateur radio operators, who use the station's transmissions to test their equipment.
Transmission system
WWV broadcasts over six transmitters, each one dedicated to a single frequency. The transmitting frequencies and time signals of WWV, WWVB and WWVH, along with the four atomic (cesium) clocks from which their time signals are derived, are maintained by NIST's Time and Frequency Division, which is based in nearby Boulder, Colorado. WWVB's carrier frequency is maintained to an accuracy of 1 part in 1014 and can be used as a frequency reference. The broadcast time is accurate to within 100 ns of UTC and 20 ns of the national time standard.
The transmitters for 2.5 MHz and 20 MHz have an ERP of 2.5 kW, while those for the other three frequencies use 10 kW of ERP. Each transmitter has a dedicated antenna, with a height corresponding to one-half of its wavelength, and an omnidirectional signal radiation pattern. The top half of each antenna tower has a quarter-wavelength radiating element, and the bottom half uses nine guy wires, connected to the midpoint of the tower and sloped at one-to-one from the ground—with a length of times the wavelength—as additional radiating elements.
Telephone service
WWV's time signal can be accessed by telephone by calling +1 (303) 499-7111 (WWV). Telephone calls are limited to 2 minutes, and the signal is delayed by an average of 30 milliseconds due to telephone network propagation time.
History
Establishment
The earliest formal record of WWV's existence is in the October 1, 1919 issue of the Department of Commerce's Radio Service Bulletin, where it was listed as a new "experimental station" assigned to the Bureau of Standards in Washington, D.C, with the randomly issued call letters of WWV. However, there were also earlier reports of radio demonstrations by the Bureau, starting the previous February.