Time signal transmitter
As time signal transmitters one is transmitting station designates which emits the currently valid time as information in maschinenverarbeitbarer (digital) form. This signal can be received with suitable clock systems or receiving devices, so that a reliable and automatic setting of the receiving radio clocks is achieved.
Depending on the requirements, a time service and its time signal transmitter can only be in operation at certain operating times - such as the Russian beta system - or 24 hours a day - such as the German long-wave transmitter DCF77 or the French transmitter Allouis . There are regular short breaks in transmission for service purposes .
Most time services send a continuous series of "seconds dots" that have a minute identifier at the second 0 (or 59) . Some services (for example in Russia) send tenths of a second points in addition to seconds. Most of the time, the transmitters encode additional information such as the hour, calendar date, weekday or the time correction dUT1 due to the irregular rotation of the earth.
General information on time signals
Modern time signals have a very high level of accuracy, reaching down to nanoseconds (billionths of a second). However, this accuracy can only be used if the transit time of the radio signal from the transmitter to the receiver is taken into account - that is, around 1 ms (0.001 s) per 300 km distance.
Due to the large range, the time signals are usually sent in the long , medium or short wave range . But there are also individual radio services on ultra-short waves (VHF) and in the transition from long to long waves , as well as using satellites in the high frequency range of micro and decimeter waves . Time information for navigation purposes used to be broadcast by LORAN transmitters, which are now being replaced by modern navigation satellites - in particular GPS , GLONASS and the emerging Galileo system.
In the pre-digital era in particular (up to the 1970s), the carrier frequencies of some radio stations were also evaluated as frequency standards. The transmitters broadcast a normal radio program, and the time receiver only synchronized itself to this carrier frequency, and the oscillations then had to be counted on site. An example of such a standard frequency transmitter was Radio Hilversum in the Netherlands.
Alternative time signal services
There are other electronically evaluable sources for time information in the radio data system of VHF radio stations (as information accompanying the normal radio program) and in the teletext and EPG data of television stations. There are also time servers on the Internet with the Network Time Protocol , which you can use to synchronize the clock in your own computer. Time information is also contained in the GPS signal, see GPS time .
The public telephone time services are outdated . They lag behind radio services in terms of precision.
Cell phones can receive and display time information over the cellular network.
On the technology of the time signal transmitter
Time signal transmitters, official designation normal frequency and time signal radio stations , basically work on radio frequencies that are usually internationally coordinated and protected. The allocation of the frequency Nominal explicitly only can be done in frequency ranges that the standard frequency and time signal radio service or the standard frequency and time signal-satellite service are assigned.
The radio stations of the time services span a frequency range of around 25 kHz to 30 MHz , i.e. long, medium and short waves. If you include the GPS time service, frequencies in the GHz range are even represented.
On the one hand, the radio range of the signal depends on the wavelength , and on the other hand, the required antenna size and operating energy. The systems are designed in such a way that the time signal service is complex, but its use is less so.
A separate radio transmitter does not necessarily have to be operated for a time signal service; the relevant information can also be transmitted with the help of the AMDS via conventional radio transmitters in the long, medium or short wave range. A French time signal service makes use of this possibility, which uses the long-wave transmitter from France Inter in Allouis (transmission frequency: 162 kHz). Austria's Ö1 (VHF) and an Italian time signal service on the medium-wave transmitter in Milan (transmission frequency: 900 kHz) offer similar services. Furthermore, time information can be obtained from the signals of many navigation systems such as LORAN-C and GPS.
All important time signal services are networked with the highest precision so that they match worldwide (apart from the signal propagation time) in the range well below nanoseconds - see the time systems UTC ("World Time"), TAI , TT and the coordination by the international earth rotation service IERS . Therefore, a high level of accuracy is also guaranteed on the user side:
Electronically, accuracies down to nanoseconds are no exception; The GPS receivers used in geodesy today already have built-in systems for time analysis to at least 0.1 ns (10 −10 seconds), which is only 3 cm at the speed of light of 299 792 km / s.
The classic time signal transmitters are mostly coupled with precise atomic clocks, which are continuously compared with those of the other time services using special procedures. For example, the line frequency of (analog) television signals or the LORAN radio beacons of long-range navigation could serve for this purpose . Direct leased lines are also used for this, or time transmission via earth satellites.
Until the 1950s, many transmitters were controlled by astrometric measurements of star passages and controlled with this technology until around 1975. Since then, atomic clocks have been developed so precisely that the accuracy of astrometry (with about 0.0005 seconds) was no longer sufficient and could be replaced by satellite methods. This means that the international time system - the “ atomic time ” TA (Temps Atomique) - is precisely defined to at least nanoseconds without interruption.
The American time signal transmitters WWV, WWVB and WWVH operated by NIST transmit their time signals in the IRIG H standard .
The frequency standards, which provide a high-precision oscillation frequency , are a preliminary stage of the time signal transmitter . The receiver then only needs to be set to the correct time (in another way) and then counts the oscillations of the frequency standard in order to update its time. On the one hand, radio transmitters with their carrier frequency, for example a long-wave transmitter with exactly 150 kHz, serve as the time standard; on the other hand, the power grid with its 50 or 60 Hz is also used. In the latter case, a synchronous clock serves as a "receiver". This technology is still in use today to a lesser extent.
history
In Germany in 1906 at the Königlich Geodätisches Institut Potsdam, tests were carried out which looked at the applicability of radio telegraphy for determining longitude. From around 1908 until the beginning of the First World War, there were international efforts for a common time symbol. From 1912 it is known that the German coast radio station in Duala ( Cameroon ) was involved in the wireless longitude determination for border regulations in Africa .
The first radio telegraphic time signal was sent from the Camperdown Signal Station in Halifax in 1907 . The first German radio station with time signals was the Norddeich coastal radio station , which began broadcasting in 1910. From March 1910, two GMT time signals were sent daily .
From 1917 on, the major radio station in Nauen took over the transmission of the signal; it was triggered initially from the Bergedorf observatory , and later from the Deutsche Seewarte in Hamburg. The shutter release clocks in Hamburg provided such a precise signal that the daily correction by astronomical precision clocks was only a few hundredths of a second. Devices that were permanently set to a wavelength of 3100 m were sold as receivers for the Nauen signal. This required individual permits from the Reich Telegraph Administration.
A Telefunken time signal receiver from the early 1920s, for example, was named E49b. In 1923 45 stations around the world broadcast the world time signal.
After the first public clock with a DCF77 receiver was installed in the city of Vienna in 1987, the company switched to GPS in 2002, which is less sensitive to electromagnetic interference . The daylight saving time changeover is regulated by a time table in the control logic.
List of time signal transmitters
- The currently only time signal transmitter in German-speaking countries is in Mainflingen near Frankfurt am Main ( call sign DCF77 , 77.5 kHz , official time and calendar switching from Germany)
- All over Eurasia , some Russian shortwave transmitters can be received on the frequencies around 5, 10 and 15 MHz (signals mostly in 0.1 s rhythm).
- In addition to the usual time announcement , many telephone services also offer more precisely defined signals. They usually consist of continuous "second points" that allow acoustic accuracies of up to a few milliseconds , electronically up to around microseconds.
Former broadcasters in the immediate vicinity were:
- from 1917 to around 1995 in Nauen near Berlin (call sign DIZ , first long wave with 77 kHz, from 1935 short wave with 4525 kHz)
- from 1966 to 2011 with Prangins in western Switzerland (callsign HBG , 75.0 kHz, official time in Switzerland)
- until around 1995 near Prague in the Czech Republic ( OMA , 50 kHz)
In alphabetic order
| Callsign | Location | Frequencies (kHz) | Beginning | The End |
|---|---|---|---|---|
| beta | Russia | 25th | ||
| BPC | China | 68.5 | ||
| BPL | China | 100 | ||
| BPM | China, Lintong ( Xi'an ) | 2500, 5000, 10,000, 15,000 | ||
| CHU | Canada , Ottawa | 3330, 7850, 14670 | ||
| DCF77 | Germany , Mainflingen | 77.5 | 1973 | |
| DIZ | Germany, Nauen near Berlin | 4525 (until 1935: 77) | 1917 | ~ 1995 |
| FTH42, FTA91 |
France , Pontoise and Lyon (from 1960 Saint-André-de-Corcy ) |
7428, 91.15 |
set | |
| HBG | Switzerland , Prangins | 75 | 1966 | 2011 |
| IBF | Italy , Turin | 5000 | ||
| JJY | Japan , Mount Ōtakadoya | 40 | ||
| JJY | Japan, Mount Hagane | 60 | ||
| MIKES | Finland , Espoo | 25,000 | ||
| MSF | United Kingdom , Anthorn | 60 | 1950 | |
| NSS | USA , Annapolis Md | 21, 5870 ... 16 180 | ~ 1990 | |
| GRANNY | Czech Republic , Prague | 50 | 1990 | |
| RBU | Russia , Taldom | 66.66 | ||
| RTZ | Russia, Irkutsk | 50 | ||
| RWM | Russia, Moscow | 4996, 9996, 14 996 | ||
| TDF | France , Allouis | 162 | 1977 | |
| WWV | United States , Fort Collins | 2500, 5000, 10,000, 15,000, 20,000 | ||
| WWVB | United States, Fort Collins | 60 | ||
| WWVH | USA, Hawaii , Kekaha | 2500, 5000, 10,000, 15,000 | ||
| YVTO | Venezuela , Caracas | 5000 |
See also
- Time measurement , resolution , code , frequency counter , clock errors
- Astronomical refraction , zenith lag
- Maser , Time Standard , International Astronomical Union , International Union for Geodesy and Geophysics
Web links
literature
Gerd Klawitter: Zeitzeichenensender , Siebel Verlag Meckenheim, 1992, ISBN 3-922221-61-0
Individual evidence
- ^ Rudolf Krug: From the beginnings of the time sign. In: Archive for German Postal History 2/1974. Frankfurt / M., P. 112.
- ↑ Peter Payer: Auf der Höhe der Zeit , diepresse.com, September 23, 2011; The press, September 24, 2011
- ↑ Christopher Wurmdobler: Do the dice roll? In: Falter 13/2007 of March 28, 2007 ( Memento of January 3, 2009 in the Internet Archive )
- ↑ Clocks put forward by one hour , wien.orf.at, March 29, 2009