Logo der PTB - Messen, Forschen, Wissen
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.

Dissemination of Time

Working Group 4.42


The Working Group 4.42 is providing accurate time to Germany. Hereby the realization of the national reference time scale UTC(PTB) is the basis of all activities and is done jointly with Working Group Time Standards.

 Alike to about 70 timing institutes scattered world- wide, PTB contributes with its atomic clocks to the realization of International Atomic Time TAI by BIPM (Bureau international des poids et mesures). This requires that UTC(PTB) is regularly compared via international time- and frequency comparisons with practically all other timing institutes world-wide. Therefore we have numerous international contacts and are frequently invited to cooperate in leading roles in the various working groups of the Consultative Committee for Time and Frequency (CCTF)

 UTC(PTB) is the basis for legal time in Germany. An important task with large impact in the public is the dissemination of legal time using different methods.

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In cooperation with various institutes our working group is striving for an improvement of the performance of satellite-based time comparisons.

Starting 2010 the time scale UTC(PTB) has been realized using an active hydrogen maser as physical source, steered with respect to the very accurate and long-term stable caesium fountains. In the meantime, other institutes have followed our example as one can see here.

Not far from now, a communication terminal reaching to the International Space Station will be put in operation in PTB. This will allow time comparisons between PTB and the Atomic Clock Ensemble (ACES) in Space with unprecendented accuracy. In early 2016 one can see structures of the ground terminal  on a roof of a high building of PTB, waiting for completion with the electronics inside. 

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The dissemination of legal time is prerequisite for the availability of accurate time in our country (and beyond).

Radio-controlled clocks are very popular in Germany and in common usage. Signals of the long-wave transmitter are received by estimated 100 million receivers in Germany and almost all over Europe.

Of similar significance ist he time dissemination vie the Internet that is pursued by our colleagues from PTB’s IT-sector (Q.42). Our group provides the timing information that is then distributed using the Network Time Protocoll (NTP).

A few staff members of our group are active as technical consultants for the Deutsche Akkreditierungsstelle DAkkS. In total 60 accreditated calibration laboratories with time and frequency activities are supervised thereby in Germany.



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WG 4.42 provides a large set of measurement data that can be used for obtaining traceability of local measurements to the national standard and to legal time. Access is via ftp.ptb.de/pub/time.

The folder "bulletins" contains the weekly Time Service Bulletin (filename  ptb_JJJJ_WW.tsb, WW: week number of the year, JJJJ year number). It contains the difference between Galileo System Time, GPS time and time disseminated via DCF77 with respect to UTC(PTB) and to UTC.

Another type of bulletin is ptb_JJJJ_MM.dcf (MM = number of the month) and log_JJJJ.dcf which inform about the properties and service interruptions of the DCF77 transmitter.

In the sub-folder /EFR one can find the documentation of the monitoring of time transmissions by the long-wave transmitters of the Europäischen Funkrundsteuerung EFR (www.efr.de/efr-system/) (European ripple control).

The folder "GNSS" contains up-to-date GNSS observation data. The sub-folders contain data in format CGGTTS and RINEX. A Readme-file in the main folder explains the use of the data.


No leap second in 2021

Time that governs our daily life is derived from Coordinated Universal Time UTC, realized using atomic clocks. Earth rotation provides another time scale, mean solar time, designated as UT1. Both time scales shall not deviate by more than one second, and leap seconds are thus introduced in UTC. The difference between the two scales, called DUT1, thus oscillates around zero with a maximum divergence of +/- 0.9 s. In the graph DUT1 is plotted and we note the introduction of the recent two leap seconds, summer 2015, and end of 2017. The steepness of the “stairs” gives a clue on the rotation of the Earth: the steeper the more slowly rotates the Earth. IERS announced in its Bulletin C62, dated 2021-07-05, that no leap second is going to be inserted at the end of 2021. The trend in DUT is quite unusual. An explanation can be seen in the lower plot showing the quantity LOD (Length of Day). LOD represents the rotation period of the Earth minus 86400 SI-seconds. LOD was observed negative for a substantial period during the last two years, the Earth rotated quite fast.

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