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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.

International Time Comparisons

World map with time institutes that contributes to the realisation of Coordinated Universal time UTC

PTB, like about 85 other institutes distributed over many countries of the world, contributes with its atomic clocks to the realization of the International Atomic Time TAI by the BIPM (Bureau international des poids et mesures). This requires comparing UTC(PTB) via international time and frequency comparisons with practically all other time institutes worldwide. Each of the institutes chooses one of its clocks as a local reference and gives the designation UTC(X) to the sequence of second ticks it emits - the X stands for the institute name. Radio signals are used to compare these different time scales with each other, so that the time differences between them are known with an uncertainty of a few billionths of a second. These comparisons are made in a comparatively simple structure: The BIPM evaluates the collected measured values of all institutes in comparison with those of PTB. This was not always the case and does not have to remain so. The choice of the "pivot" fell on PTB years ago because it is geographically favorably located and thus allows to form a bridge between the continents, generates itself a very stable time scale UTC(PTB) and operates all the required technical facilities for time comparisons.

The figure shows the distribution of the world's time institutes. Institutes marked in red are compared with PTB via signals of the satellite navigation systems GPS, to a lesser extent GLONASS and Galileo. Institutes marked in green additionally operate facilities for time comparison by means of radio signals which are sent back and forth between the institutes concerned by the same type of satellite as is used for television transmissions, so-called Two-Way Satellite Time and Frequency Transfer. All these comparisons are carried out around the clock and the results are sent to the International Bureau of Weights and Measures (BIPM) daily.