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A modern LF radio-controlled clock. A radio clock or radio-controlled clock (RCC), and often colloquially (and incorrectly [1]) referred to as an "atomic clock", is a type of quartz clock or watch that is automatically synchronized to a time code transmitted by a radio transmitter connected to a time standard such as an atomic clock.
The master clock in a clock network can receive accurate time in a number of ways: through the United States GPS satellite constellation, a Network Time Protocol server, the CDMA cellular phone network, a modem connection to a time source, or by listening to radio transmissions from WWV or WWVH, or a special signal from an upstream broadcast network.
The telegraphic distribution of time signals was made obsolete by the use of AM, FM, shortwave radio, Internet Network Time Protocol servers as well as atomic clocks in satellite navigation systems. Time signals have been transmitted by radio since 1905. [12] There are dedicated radio time signal stations around the world.
Digital clocks typically use the 50 or 60 hertz oscillation of AC power or a 32,768 hertz crystal oscillator as in a quartz clock to keep time. Most digital clocks display the hour of the day in 24-hour format; in the United States and a few other countries, a commonly used hour sequence option is 12-hour format (with some indication of AM or PM).
In the United States, the United States Naval Observatory provides the standard of time, called UTC(USNO), for the United States military and the Global Positioning System, [1] while the National Institute of Standards and Technology provides the standard of time for civil purposes in the United States, called UTC(NIST).
Clock signal and legend. In electronics and especially synchronous digital circuits, a clock signal (historically also known as logic beat) [1] is an electronic logic signal (voltage or current) which oscillates between a high and a low state at a constant frequency and is used like a metronome to synchronize actions of digital circuits.
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Specifically, it refers to the technique of having the transmitting device send a clock signal along with the data signals. The timing of the unidirectional data signals is referenced to the clock (often called the strobe) sourced by the same device that generates those signals, and not to a global clock (i.e. generated by a bus master).