Difference Atomic Clock - Radio Clock

With this page we would like to explain the difference between "atomic clocks" and "radio clocks", because some manufacturers refer to their radio-controlled clocks as "atomic clocks", which isn't really true.

Atomic Clocks

An atomic clock is a time counter, wich is controlled by the frequency oscillation of certain atoms (e.g. cesium, rubidium), which are energized by an electromagnetic field or optical pumping. The first atomic clock was developed by the American Isidor Isaac Rabi (1898-1988) at the Columbia University, who got the nobel price for this development in 1944.

pic. atomic clock Nowadays there are a lot of atomic clocks, mostly for research purposes.
Here are some links to atomic clocks of newer design. (cesium-fountains) :

In Germany the transmitted frequencies and signals are derived from the atomic clocks of the Physikalisch-Technische Bundesanstalt (PTB) Germany, the national institute for science and technology and the highest technical authority of the Federal Republic of Germany concerning metrology and physical safety engineering in Germany.

The control signal is not transmitted from Braunschweig via lines, as is often assumed, but is generated in situ with the aid of a control device designed by PTB and monitored from Braunschweig. After the DCF77 signal generated by the PTB facilities has been conducted to T-Systems Media Broadcast, this company is responsible for emitting it via the transmitting and antenna facility operated by it. In Germany the signal is transmitted with a radius about 1500 km by the low frequency transmitter DCF77 on 77.5 kHz, with an accuracy about one second in a million years.

Radio Clocks

A radio clock has a RF receiver that receives the signal from a transmitter that gets the time from a real "atomic clock". Radio clocks actually have a built-in miniature radio receiver, which is permanently tuned to receive the 77.5 kHz signal, and a microcontroller that decodes the radio signal. Once your radio-controlled clock has decoded the signal from DCF77, it will synchronize its own clock to the time signals received by radio.


atomic clock - radio clock