The WWV time signals are a portion of a broadcast from the U.S. National Institute of Standards and Technology's HF radio station that are used to disseminate the official U.S. time. The time signals ensure that uniform time is maintained throughout the United States and around the world.
The U.S. National Institute of Standards and Technology's call sign is WWV. Once every minute, WWV broadcasts a voice announcement of the time. The time signals are based on cesium atomic frequency standards and allow time-keeping devices such as radio-controlled clocks to automatically maintain accurate time without the need for manual adjustment.
WWV broadcasts standard frequency audio tones that alternate during most minutes of the hour. They usually feature a 500 or 600 Hz audio tone.
WWV has been broadcasting second pulses since 1937. Voice announcements started on Jan. 1, 1950, and were broadcast every five minutes. WWV moved to Fort Collins, Colorado, in 1966. This allowed better reception of its signal throughout the continental United States. The station adopted Coordinated Universal Time in 1974.
WWV also broadcasts time signals derived by astronomers who monitor the speed of the Earth's rotation. These signals are used in applications such as navigation and satellite observations of the Earth.