Logo of the Physikalisch-Technische Bundesanstalt
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

Profile

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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Research/Development

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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Services

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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Information

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.

Starting in early 2022, the access to the published bulletins is as follows:
The weekly Opens internal link in current windowTime Service Bulletin (filename  ptb_JJJJ_WW.tsb, WW: week number of the year, JJJJ year number) contains the difference between Galileo System Time, GPS time and time disseminated via DCF77 with respect to UTC(PTB) and to UTC.

The monthly DCF77-bulletin (file name ptb_JJJJ_MM.dcf (MM = number of the month) and the continuing file log_JJJJ.dcf which inform about the properties and service interruptions of the DCF77 transmitter can be accessed Opens internal link in current windowhere.

The PTB has concluded a cooperation agreement with the company EFR GmbH, which stipulates that EFR time signals are also monitored by the PTB. The transmitters concerned are DCF39, DCF49 and HGA22. The results of the comparison with the legal time are published in weekly Opens internal link in current windowEFR bulletins (name: ptb_YYYY_WW.efr (WW= week of the year)). Information material is available in the same directory.

For the time being, bulletins can only be retrieved using the links to the PTB website.

Last but not least, PTB makes current measured values of several GNSS receivers available. The previous access via an ftp server (ftp.ptb.de) will be replaced by a sftp server (sftp.ptb.de) for IT security reasons. To get access, interested parties must identify themselves with username and password. Please contact Opens local program for sending emailtime(at)ptb.de to obtain access authorization. You will find files in CGGTTS format as well as RINEX 2.1x and partly also format 3.x. A READ_ME file in the main directory gives instructions on how to use the files.

News

No leap second in 2022

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 C64, dated 2022-07-05, that no leap second is going to be inserted at the end of 2022. The trend in DUT is quite unusual. An explanation can be seen in the plot to the right, 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.

Difference between mean solar time UT1 and Coordinated Universal Time UTC
Length of day from 2019 to 2022

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