Ideal Wall Clocks

A radio clock or radio-controlled clock is a clock that is synchronized by a time code bit stream transmitted by a radio transmitter connected to a time standard such as an atomic clock. Such a clock may be synchronized to the time sent by a single transmitter, such as many national or regional time transmitters, or may use multiple transmitters, like the Global Positioning System. Such systems may be used to set computer clocks or clocks meant for human readability, or for any purpose where accurate time is needed.

Radio clocks synchronized to terrestrial time signals can usually achieve an accuracy of around 1 millisecond relative to the time standard, generally limited by uncertainties and variability in radio propagation.

Longwave and shortwave transmissions

Radio clocks depend on time signal of radio stations. These time standards specify:

• the broadcast frequency of the frequency standard
• the exact geographic location of each antenna, so the radio signal’s time of propagation can be estimated
• how the beginning of each second interval is determined
• how the signal is modulated to identify the current time

In the UK the radio clocks are synchronised with GMT time