1. DCF system - synchronization with absolutely correct time.
DCF77 is a longwave time signal and standard-frequency radio station. Its primary and backup transmitter are located at in Mainflingen, about 25 km south-east of Frankfurt am Main, Germany. DCF77 has been in service as a standard-frequency station since 1959; date and time information was added in 1973. The 77.5 kHz carrier signal is generated from local atomic clocks that are linked with the German master clocks in Braunschweig. With 50 kW high power, the station signal can be received in large parts of Europe, as far as 2000 km from Frankfurt.
2. GPS system-synchronization with absolutely correct time.
The Global Positioning System (GPS) is a satellite-based system that can be used to locate positions anywhere on the earth. There are now at least 24 satellites orbiting the earth at an altitude of about 11,000 nautical miles. The high altitude insures that the satellite orbits are stable, precise and predictable, and that the satellites' motion through space is not affected by atmospheric drag. 24 satellites make up a full GPS constellation.
3. DHF system - wireless clock system
Synchronization of a network of clocks in one or more buildings without connecting the clocks with cables. The master clock sends a time code via an 869 MHz radio transmitter.
The slave clocks capture the time message and are synchronized automatically. If there is any interference, they will continue to work on their own time base. The signal has a range of around 100 to 200 meters. Getting rid of cables means major savings can be made in the installation and provides great freedom of location.