The time signal

Legal time (1) (on the territory of the French Republic is fixed by reference to Coordinated Universal Time (UTC) established by the International Bureau of Weights and Measures (BIPM) as part of the General Conference on Weights and Measures.

Once established by the Paris Observatory, this legal time is made available to various users in the form of information that can be used by electronic devices (radar, computers, traffic lights, aircraft, etc.). Once received by the equipment in question, this signal makes it possible for it to be synchronised extremely precisely with other electronic equipment and therefore not to drift in time.

Having a time signal that allows all equipment concerned to be synchronised is therefore essential for the life of the nation, especially in areas impacting security.

This information can be made available in various forms: by GNSS-type satellite (GPS, Galileo, etc.), by Internet via NTP (Network Time Protocol), perhaps in the near future via 5G base stations and finally by terrestrial radio (radio transmitter).

The Agency manages the terrestrial broadcasting of legal time data in mainland France. This mission has been in its remit since 1st January 2019 assigned by the so-called "ELAN" Act (article 233 of Act no. 2018-1021 of 23 November 2018).

This reference time signal based on atomic clocks and accurate to less than a millisecond, provides French legal time by terrestrial radio when received by an appropriate device.

Broadcasting is provided by TDF from its Allouis site in the Cher département, in compliance with the NF C 90-002 standard relating to data broadcasting systems compatible with amplitude modulation sound broadcasting.

The time base for the time signal is provided by the Paris Observatory in cooperation with the Laboratoire National d'Essais (LNE) and the France Horlogerie trade association

Until 31 December 2016, this over-the-air broadcast was encapsulated in France Inter's long-wave radio programmes on the 162 kHz frequency.

The importance of this hourly broadcast led to its continuation beyond this deadline and, since then, the legal time signal has continued to be broadcast on the same frequency and from the same site. Indeed, this signal is needed for many of the uses mentioned above, and in practice synchronises over 200,000 clocks in France.

As part of its missions, the Agency is in charge of optimising the technical system, informing users and assessing the system in the light of future developments in technical broadcasting methods. If the decision were taken, the ANFR would also be in charge of implementing the switch-off of this broadcasting.


1 Legal Time on the territory of the French Republic is fixed by reference to Coordinated Universal Time (UTC). The Paris Observatory is in charge of establishing the local value of UTC and providing it to users in the form of a time signal.