Logo PTB
View of the Mainflingen long-wave radio station for transmission of the DCF77 signal: transmitter building (in the back), antenna building (yellow bricks) and antenna masts.

Benefit of DCF77

DCF77 radio-controlled clocks for private use evaluate the time code transmitted via AM, here: a small selection (without demand for completeness)

For many years, the long-wave radio transmitter DCF77 at 77.5 kHz controlled by PTB has been available as a reliable time signal and standard frequency transmitter, which can be received in wide parts of Europe. With the aid of the carrier frequency of DCF77, standard frequency generators are calibrated or automatically readjusted. Time-keeping systems at train stations, in the field of telecommunication and information technology, at radio and TV stations are radio-controlled by DCF77 as well as tariff change-over clocks of energy supply companies and clocks in traffic light facilities. Meanwhile, according to absolute numbers, the most frequent users are private persons: Radio-controlled clocks are used to an ever increasing extent (as wristwatches, alarm clocks, long-case clocks and wall clocks). To dispose of the correct time, estimates to the second or millisecond are made.

However, the success of the radio-controlled clock has especially to do with the characteristics of the emission via long wave. Compared to time-transmission via satellites, long-wave signals have a decisive advantage: they penetrate into buildings and their reception is not appreciably impaired by obstacles such as trees or tower block buildings. They can be received without exterior antennas, in particular with small ferrite antennas incorporated in the case of radio-controlled clocks. Due to this property of the long wave, compact radio-controlled clocks operated with battery or solar cells can be designed and operated without cable connection to an external antenna. In contrast to this, the reception of signals of the navigation system GPS, and in future of the European equivalent Galileo, requires an exterior antenna, with a sight to the sky as free as possible. If this antenna can be installed, undeniably smaller uncertainties can be reached in time transmission. Time transmission via satellite and time propagation on long wave will therefore not replace but complement each another.