General information
In order to transmit the exact time of an atomic clock e.g. to radio clocks (radio wristwatches, radio wall clocks or radio alarm clocks) but also to radio and TV transmitters there are worldwide different time signal transmitters. They are special transmitters that are usually linked to the atomic clock and transmit the current time as information in digital form to suitable reception facilities. The time signals have a large range, which are transmitted in the long, medium or short wave range. Thus the correct time is always displayed on the clocks and devices within range of the transmitters. In most cases, they also transmit coded information on the calendar date and weekday, so that these are always up to date.
The time signal services are networked with the highest precision, so that they match worldwide in the range far below nanoseconds.
Suction. Multifrequency radio clocks can even receive the signals of several time signal transmitters (usually DCF, MSF, JJY and WWV) and thus synchronise the time in large parts of the world.
Important international time signal transmitters
The most important time signal transmitters that make this signal available to the public:
- DCF77 (Germany) in Mainflingen in Hessen
- MSF (Großbritannien) in Anthorn
- JJY (Japan)
- WWV (USA) in Fort Collins, Colorado
- WWVH (USA) in Hawaii
- BPC (China) in Shangqiu
Range and accuracy
The range of the time signal transmitters depends on the frequency used, the size of the antenna and the transmitting power. In addition, the range of radio waves is also influenced by various factors. For example, under certain conditions they can be reflected by the troposphere (e.g. in inversion weather conditions) or the ionosphere, resulting in so-called overreach.
The DCF77 signal has a range of about 2000 km - at over-ranges up to about 6000 km - and is therefore available practically throughout Europe.
Since - unlike e.g. time signals from GPS satellites - the offset caused by the signal propagation time is not taken into account and electromagnetic waves move through space at the speed of light, the signal deviates from the actual time by about 0.001s per 300 km distance.
A sufficient accuracy for the synchronization of your radio-controlled clock...
Other time signal transmitters
In addition to the time signal transmitters described, there are a number of other options for receiving time signal signals:
- The Network Time Protocol (NTP) is a standard used for time synchronization on the Internet.
It is provided by various NTP servers - for example, an NTP server is operated by the Physikalisch-Technische-Bundesanstalt, which also transmits the DCF77 time signal. Other devices connected to the Internet can retrieve this signal and synchronize it with the exact time. Uhrzeit.org also uses this service to display the time.
- GPS navigation uses the time signals from GPS satellites. This system works highly precisely with a maximum rate deviation of one microsecond.
- The Radio Data System (RDS), which is used by radio stations to transmit additional information to the radio programme (e.g. which song they are currently listening to on the radio), is also used to transmit time signals.
- Digital Audio Broadcasting (DAB) also transmits a time signal that can be used by radios.
- Televisions can display the time using teletext and EPG data.
- ...and also the good old time announcement by telephone still exists - even if it does not reach the precision of other time signals and is difficult for devices to evaluate. A time announcement can be reached by calling 0180 4100100, but this service is subject to a charge.
A time announcement at the normal telephone rate can be reached under the Hamburg telephone number +49 40 428990.
