Radio controlled clock
A radio clock is a quartz watch that can receive a radio time signal from a time signal transmitter and uses this information to readjust the internal quartz watch.
functionality
The heart of the unit is the straight-ahead receiver for receiving the time signal from a long-wave transmitter . Time signal transmitters include DCF77 in Mainflingen near Frankfurt am Main , MSF in England, Allouis transmitter in France, the former HBG in Switzerland, JJY in Japan and the American time signal transmitter WWVB . The ferrite rod antenna used to receive signals in radio clocks can be seen in the picture (glued into the green back wall). Right is on the ferrite coil and directly soldered to the capacitor (red) for resonant circuit tuning to the transmitting frequency. The antenna is about the size of a " Mignon " size battery cell . It should be noted that every ferrite antenna has a polarization and directional effect and must therefore be oriented horizontally and transversely to the direction of the transmitter. If you ignore this, the signal strength may be too weak to effect synchronization.
There are typically two integrated circuits (ICs) on the clock's motherboard . A clock IC takes care of the clock's functions, the second "radio" IC is supplied with the radio signal from the antenna and forwards the received clock and data signals to the clock IC.
accuracy
Although the time signal is sent continuously, it is often only queried occasionally to readjust to save energy. For watches that are operated with larger cells, a reception is usual every hour on the hour, for wristwatches with button cells or with solar cells only once a day, usually between 1:00 and 4:00 in the morning. This is enough to meet the response errors to correct the quartz watch. An example of clocks that are synchronized with the radio time signal every minute are the master clocks of the German station clocks .
Outside of the time signal reception range or if the signal is disturbed or switched off, a radio clock continues to run like any other quartz clock. This is where the rate error common in quartz watches (the voltage of the clock rate ) becomes noticeable. When a time signal is received again, the clock is reset immediately and then displays the time transmitted by the time signal transmitter; this is usually the legal time , which differs from Coordinated Universal Time by exactly a whole number of hours. Due to the narrow-band receivers and the internal processing speed of the electronics, the time is usually displayed with a slight, constant delay ( latency ), which is usually 0.1-0.4 s.
variants
Radio clocks are widely used as wall clocks and wrist watches . An extension of the radio clock is the radio alarm clock , the main function of which is the alarm function.
Radio clocks for PCs
The internal clock of a PC can be synchronized via a radio clock. This can be built into the device or connected externally. One variant is, for example, a small battery-operated radio clock that is located in the printer cable like a dongle and sets the time of the PC clock by command or at fixed time intervals. Alternatively, radio clocks are available for connection to USB. This technology has largely been replaced by NTP , but is still useful for computer systems that are not permanently connected or not connected to the Internet at all.
Using a sound card that can sample at 192 kHz, it is possible to decode time signal signals using SDR software and to use them to set the PC's clock.
Radio solar watch
In addition to stationary radio-controlled clocks operated with solar cells, there are wristwatches with this type of supply. There is no need to change the battery. The radio solar watch was largely developed by Karl Diehl and Karl Gebhardt. A built-in rechargeable battery supplies the clock with energy in the dark ("dark run time").
The first radio-controlled solar watches still had a relatively high energy consumption and relatively weak solar cells. Therefore, there could be an insufficient energy supply. As a men's wristwatch, modern examples have a dark lifespan of two years. Artificial light is sufficient to charge the energy store.
Advantages and disadvantages
The advantages of a radio clock are that a very precise time is always displayed, no manual readjustment is necessary. The changeover between normal zone time and daylight saving time takes place automatically if it is operated within the reception zone of the time signal transmitter. Some radio controlled clocks cannot be set manually, so that they are dependent on receiving the time signal.
Although a radio-controlled watch is usually impressive because of its precision, at least some commercially available models occasionally malfunction . These easily lead to a wrong display by hours. This is favored by the weak possibility of checking the time signal for reception errors and the fact that the long-wave signal can easily be impaired by all kinds of technical devices. In addition, in reinforced concrete buildings, reception is often only possible near the windows.
history
The digitally coded time transmission for radio clocks was registered for a patent in 1967 by Wolfgang Hilberg , who works for the Telefunken company . After his appointment as professor of electrical engineering at the TH Darmstadt in 1972, he developed the first prototypes and essential components of this type of watch.
The Physikalisch-Technische Bundesanstalt in Braunschweig began in 1973 to transmit cesium clock time signals (including calendar information and information about summer time) via the DCF77 transmitter. From 1973, large clocks with a corresponding receiver were able to adjust themselves to it with high precision. The HBG transmitter operated in Switzerland from 1966 to 2011, which operated with a carrier frequency of 75 kHz, was compatible with DCF77.
Time signal transmitters that work in a similar manner are located in many countries around the world. In most cases, different carrier frequencies and different encodings, such as the IRIG time code common in the USA, are used. Some radio-controlled watches, for example the G-Shock from Casio, can receive and evaluate time signals from several different time signal transmitters.
Radio-controlled clocks were only built in relatively small numbers for professional and semi-professional use in the 1970s , for example by Hopf. Radio controlled clocks were available to private users by the early 1980s at the latest. The Hopf mini radio clock 4300 with display of day of the week, time or date including year (switchable), display of optimal antenna alignment as well as radio or quartz clock operation cost 395 DM in 1983 as a kit , 735 DM as a finished device, which is 376 EUR according to today's purchasing power or 700 EUR.
In 1986 Telefunken (→ Atmel ) presented the first integrated circuit U2775B . On the basis of this IC it was possible for the first time to build inexpensive radio controlled clocks for the mass market. The first providers were Kundo in St. Georgen in the Black Forest and Junghans . A wristwatch-compatible IC came onto the market in 1990, which Junghans built into the world's first radio-controlled wristwatch, the MEGA 1 .
Manufacturers of industrial radio clocks and synchronization software are Gude, Hopf, Linum and Meinberg.
In radio-controlled wristwatches, antennas made of amorphous straps were initially integrated inside the leather straps, which occasionally led to contact problems in the transition area between the strap and the watch case. This is why miniature ferrite rod antennas were later built into the watch cases, which then had to be made of plastic or ceramic because metal would have shielded the radio waves.
Alternatives
RDS
Remote-controlled time setting is possible via radio reception ( RDS ). It is used by broadcasters sent in parallel to program a time signal, which is an integrated radio clock can automatically adjust. A frequent application are clocks coupled with the radio in passenger cars , with radio reception automatically enabling daylight saving time changes.
DAB
With digital audio broadcasting (digital radio, DAB / DAB +) a time signal is also transmitted. This is evaluated by many DAB radios to display the time.
GPS
The GPS navigation system is based on the reception of highly precise time signals from satellites. This GPS time is shifted by a few whole seconds compared to UTC . Since this shift is transmitted with the GPS signal, it can be taken into account by the GPS watch. This system guarantees a maximum rate deviation of one microsecond . With the DCF77 signal, this deviation is exceeded at a distance of 300 kilometers from the transmitter due to the runtime of the signal ( speed of light ).
NTP / PTP
Devices connected to the Internet can be synchronized with an accuracy of well under a second via the Network Time Protocol (NTP). Since NTP servers are offered, among other things, by institutions that are officially active as time keepers , synchronization with the official time is possible for everyone. Local synchronicity in the nanosecond range can be achieved for locally limited networks using the Precision Time Protocol (PTP) .
Cellular
Every cell phone mast has been transmitting a time signal since the dawn of mobile communications.
Web links
- “Atomzeit” on the website of the Physikalisch-Technische Bundesanstalt Braunschweig
Individual evidence
- ↑ DCF77 receiver to USB for radio amateurs. Retrieved October 10, 2010 .
- ↑ Michael Wöste: Amateur radio tinkering :: Tips :: Decoding DCF77 . Retrieved January 19, 2015.
- ↑ Patent DE1673793 : Method for the ongoing transmission of the time.
- ↑ hopf Elektronik GmbH
- ^ Conrad Electronic (Ed.): Conrad Electronic Catalog E 84 . 1983, p. 341 .
- ↑ These figures were based on the template: Inflation determined, rounded to the nearest full EUR and refer to the previous January.
- ↑ Journal elektronik industrie 7-2009, page 17