page_title: Time signal
section_title: Dedicated time signal broadcasts
hierarchical_section_title: Time signal / Radio time sources / Dedicated time signal broadcasts
caption_attribution_description: English: Low cost DCF77 receiver module. This is a radio receiver used in a radio clock, a quartz clock which is periodically set to the correct time by radio signals synchronized with an atomic clock from a government radio station. This one receives the coded time signals broadcast by German government time radio station DCF77 on 77.5 kHz. The ferrite loopstick (left) is the radio's antenna, and with the attached capacitor also serves as its tuned circuit. Français&#160;: Module de réception DCF77 à faible coût Deutsch: Billiger DCF77 Empfänger Modul Nederlands: Goedkope DCF77 ontvangstmodule. Dit is een radio-ontvanger zoals gebruikt in een radioklok, een kwartsklok die periodiek wordt gelijkgezet met het radiosignaal afkomstig van een overheidszender, dat wordt gesynchroniseerd met een atoomklok. Dit exemplaar ontvangt tijdcodesignalen van het Duitse radiostation DCF77 op 77,5 kHz. De ferrietstaaf met spoel (links) fungeert als ontvangstantenne; deze vormt bovendien een afgestemde kring samen met de eraan bevestigde condensator.
context_page_description: A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day.
  Church bells or voices announcing hours of prayer gave way to automatically operated chimes on public clocks; however, audible signals have limited range. Busy seaports used a visual signal, the dropping of a ball, to allow mariners to check the chronometers used for navigation. The advent of electrical telegraphs allowed widespread and precise distribution of time signals from central observatories. Railways were among the first customers for time signals, which allowed synchronization of their operations over wide geographic areas. Dedicated radio time signal stations transmit a signal that allows automatic synchronization of clocks, and commercial broadcasters still include time signals in their programming.
  Today, GPS navigation radio signals are used to precisely distribute time signals over much of the world. There are many commercially available radio controlled clocks available to accurately indicate the local time, both for business and residential use. Computers often set their time from an Internet atomic clock source.
context_section_description: 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.  Since 1905 time signals have been transmitted by radio. There are dedicated radio time signal stations around the world.
  Time stations operating in the longwave radio band have highly predictable radio propagation characteristics, which gives low uncertainty in the received time signals. Stations operating in the shortwave band can cover wider areas with relatively low-power transmitters, but the varying distance that the signal travels increases the uncertainty of the time signal on a scale of milliseconds.
  Radio time signal stations broadcast the time in both audible and machine-readable time code form that can be used as references for radio clocks and radio-controlled watches.
  The audio portions of the shortwave WWV and WWVH broadcasts can also be heard by telephone. The time announcements are normally delayed by less than 30 ms when using land lines from within the continental United States, and the stability (delay variation) is generally < 1 ms. When mobile phones are used, the delays are often more than 100 ms due to the multiple access methods used to share cell channels. In rare instances when the telephone connection is made by satellite, the time is delayed by 250 to 500 ms.
  These broadcasts are available by telephone by dialling US numbers (303) 499-7111 for WWV (Colorado), and (808) 335-4363 for WWVH (Hawaii). Calls, which are not toll-free, are disconnected after 2 minutes.
  Loran-C time signals may also be used for radio clock synchronization, by augmenting their highly accurate frequency transmissions with external measurements of the offsets of LORAN navigation signals against time standards.
caption: A low cost LF radio clock receiver, antenna left, receiver right.
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