Standard time and frequency signal service
As time signal transmitter, a special transmitter is referred to that radiates the currently valid time as information in maschinenverarbeitbarer (digital ) form. With proper clock systems or receiving devices, this signal can be received, so that a reliable and automatic adjustment of the receiving radio clocks is achieved.
Depending on the requirement, a time service and his time signal transmitter only at certain periods of operation - as the Russian beta system - be operating, or 24 hours a day, as the German long wave transmitter DCF77 or French channels Allouis. There are regular, short transmission intervals for servicing.
Send Most time services an ongoing series of " Seconds points " that have to second 0 (or 59) one minutes identifier. Some services (eg, in Russia) Send next second temporarily tenths of points. Usually the sender encode additional information such as hours, calendar date, day of week or time correction DUT1 for irregular rotation of the earth.
General to time signals
Modern time signals have a very high accuracy, up to the nanosecond range ( billionths of a second ). This accuracy, however, can only be used if the term of the radio signal from the transmitter to the receiver is taken into account - that is about 1 ms ( 0.001 s ) per 300 km distance.
The time signals are usually sent because of the large range in the area of long, medium or short wave. There are also some radio services on ultra-short wave ( VHF) and in the transition from long to very long waves, as well as via satellite in the high frequency range of micro-and decimeter. Time information for navigation were previously aired by LORAN stations, which are now being replaced by modern satellite navigation, in particular GPS, GLONASS, Galileo and the resulting system.
Especially in the pre-digital era (until the 1970s), the carrier frequencies of some radio stations were evaluated as frequency standards. Thus, the transmitter sent a regular radio program, and the time receiver synchronized only to this carrier frequency, and the counting of the oscillations had to be made on the spot itself. An example of such a frequency standard station was Radio Hilversum in the Netherlands.
Alternative time signal services
More electronic evaluation sources for time information are available at Radio Data System FM radio stations ( as accompanying information to the normal radio program ) and in the teletext and EPG data of television. Next there is the internet time server using the Network Time Protocol, by which you can synchronize the clock in your own computer.
Refit the public telephone time services. They remain in the precision behind the radio services.
Mobile phones can receive and display time information about the wireless network.
About the technology of the time signal transmitter
The broadcasting transmitter of the time services spanning a range of a radio frequency band from approximately 25 kHz to 30 MHz, that is, long -, medium and short waves. Counting the GPS time service to even frequencies are represented in the GHz range.
From the wavelength on the one hand depends on the radio range of the signal, on the other hand, the required antenna size and operating energy. The systems are designed so that while the time signal service is consuming less, however its use.
Its own radio station does not have to be operated for a time signal service. The relevant information can be transmitted over conventional broadcasters in the long, medium or short wave range with the help of the AMDS. This possibility makes a French time signal service use, the long-wave transmitter of France Inter in Allouis ( transmission frequency: 162 kHz) uses. Also Austria OE1 (FM ) and an Italian time signal service on medium wave transmitter Milan ( transmission frequency: 900 kHz) offer similar. Further, one can see time information from the signals of many navigation systems such as LORAN -C and GPS.
All important time signal services are networked with high precision, so that they world (apart from the signal propagation time) coincide in the range well below nanoseconds - see Time Systems UTC ( " Universal Time " ), TAI, TD and coordination by the international Earth Rotation Service IERS. Therefore, on the user side is a very high accuracy:
Electronic means are accuracies of up to nanoseconds no exception; in today benützten in geodesy GPS receivers systems for time analysis to at least 0.1 are already installed ns (10-10 seconds), which accounts for s in the speed of light 299792 km / only 3cm.
The classic time signal transmitters are coupled with i a precise atomic clocks, which are compared by special methods continuously with those of the other time services. These can include, for example, the internal switching codes of television signals serve, or the LORAN radio fire of long-range navigation. Also direct leased lines are used for it, or the time comparison using earth satellites.
Until the 1950s, many stations were controlled by astrometric measurements of stellar passages, and up circa 1975 controlled with this technique. Since accurate atomic clocks were developed so that the accuracy of the astrometry ( with about 0.0005 seconds) was no longer sufficient and could be replaced by satellite methods. The " atomic time " TA ( Temps Atomique ) remains well defined at least nanoseconds - This is the international time system.
Operated by the U.S. NIST time signal transmitters WWV, WWVB and WWVH send their time signal in the standard IRIG H.
A precursor of the time signal transmitters form the frequency standards, which provide a highly accurate oscillation frequency. The receiver then needs to be set only once ( otherwise) to the correct time and then counts from the vibrations of the frequency standard to update its time. As a time standard on the one hand broadcasters serve their carrier frequency, for example, a long-wave transmitter with exactly 150 kHz, on the other hand, the power grid, with its 50 or 60 Hz is used. In the latter case, a synchronization clock serves as a " receiver ". This technique is to a lesser extent still in use today.
History
In Germany in 1906 were at the Royal Geodetic Institute Potsdam carried out experiments that had the applicability of the RT for longitude determination to content. From around 1908 there was until the beginning of World War international efforts for a common time signal. From the year 1912, reported that the German coast station in Douala (Cameroon) was involved in the wireless longitude determination at border adjustments in Africa.
The first radio- telegraphic time signal was sent in 1907 from the Camperdown Signal Station, Halifax. The first German radio station with time sign was the coast station north dike, the send operation started 1910. Starting in March 1910, sent two Zeitzeichen GMT daily.
From 1917 to the large radio station Nauen took over the transmission of the signal, the resolution was carried out initially from the Bergedorf Observatory, later. From the German Naval Observatory in Hamburg The trip clocks in Hamburg delivered such a precise signal that the daily correction by astronomical precision watches only a few hundredths was seconds. As a receiver for the Nauen signal devices have been sold which were fixed at 3100 m wavelength. For this purpose, individual licenses of the Imperial Telegraph Administration were required.
A Telefunken - time signal receiver from the early 1920s, for example, had the designation E49b. Worldwide 45 stations sent the world - time mark in 1923.
After the City of Vienna in 1987 the first public clock with DCF - 77 receiver installed, it provides since 2002 on GPS, which is less sensitive to today's electro and funk holes. The time changeover is controlled by a time table in the control logic.
List of time signal transmitters
- The currently only in German-speaking countries is in Mainflingen near Frankfurt am Main (call sign DCF77, 77.5 kHz, official time and date clock from Germany )
- In Eurasia also some Russian shortwave transmitters on the frequencies 5, 10 and 15 MHz receive ( mostly signals in the 0.1 -s- rhythm).
- In addition many of telephony services in addition to the usual time announcement also better defined signals. They usually consist of continuous " Seconds points " that allow the acoustic accuracy of up to a few milliseconds, electronically to about microseconds.
Former stations in the immediate vicinity were:
- From 1917 to approximately 1995 in Nauen, near Berlin (call sign DIZ, only long wave with 77 kHz, from 1935 to 4525 kHz shortwave )
- 1966-2011 at Prangins in western Switzerland (call HBG, 75.0 kHz, official time in Switzerland)
- To about 1995 near Prague in the Czech Republic (OMA, 50 kHz)