The co-chairs of the meeting Decoupling Civil Timekeeping from Earth Rotation received the information described via a contributor.
We believe that this PDF file was produced from a copy of ITU-R Document 7/1005-E.
That should be the draft revision of Recommendation ITU-R TF.460-6 which is to be voted upon at the Radiocommunication Assembly in Geneva in 2012 January.
The remainder of this file is a crude conversion of that PDF file into HTML.
Radiocommunication Assembly (RA-12)
Geneva, 16-20 January 2012

Subject: Question ITU-R 236/7
Document 7/1005-E
20 October 2011

Radiocommunication Study Group 7
Standard-frequency and time-signal emissions

Summary of revisions
This modification of the Recommendation eliminates the procedure for adjustment of UTC by
insertion of leap seconds. The elimination of the leap second adjustments is recommended to be
effective on 1 January five years after approval of this Recommendation.

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Standard-frequency and time-signal emissions

(Question ITU-R 102/7)


This Recommendation defines the implementation of Coordinated Universal Time (UTC) without leap
second adjustments. UTC serves as the time and frequency reference of standard-frequency and time-signal

The ITU Radiocommunication Assembly,


a) that Article 5
of the Radio Regulations allocates bands of frequencies to the standard-frequency and time-signal service;

b) the provisions of Article 26 of the Radio Regulations;

c) the continuing need for close cooperation between Radiocommunication Study Group 7
and the International Maritime Organization (IMO), the International Civil Aviation Organization
(ICAO), the General Conference of Weights and Measures (CGPM), the Consultative Committee
for Time and Frequency (CCTF), the Bureau International des Poids et Mesures (BIPM), the
International Earth Rotation and Reference Systems Service (IERS) and the concerned Unions of
the International Council of Scientific Unions (ICSU);

d) the importance of maintaining worldwide coordination of standard-
frequency and time-signal emissions;

e) the need to disseminate standard frequencies and time signals in conformity with the SI
(International System of Units) second as defined by the CGPM;

f) that in 1975 the CGPM recommended the use of UTC as the basis of civil time;

* This Recommendation should be brought to the attention of the International Maritime
Organization (IMO), the International Civil Aviation Organization (ICAO), the General Conference
of Weights and Measures (CGPM), the Consultative Committee for Time and Frequency (CCTF),
the Bureau International des Poids et Mesures (BIPM), the International Earth Rotation and
Reference Systems Service (IERS), the International Union of Geodesy and Geophysics (IUGG),
the International Union of Radio Science (URSI), the International Organization for Standardization
(ISO) and the International Astronomical Union (IAU).

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g) that other scientific organizations, particularly the International Astronomical Union
(IAU) and the International Union of Radio Science (URSI), have recommended the general use of

h) the importance of monitoring the difference between the UTC time-scale and the time
defined by the rotation of the Earth (UT1) and maintaining the respective knowledge-base;

j) that the IERS provides updated daily data relating the UT1 to UTC to users;

k) that the IERS provides predictions of the difference between UT1 and UTC at different
delays, which allow real-time access to UT1, and which will on average over a two-year period
provide a more accurate knowledge of UT1 than does UTC with leap seconds,


that Recommendation ITU-R TF.460-6 is incorporated by reference in the Radio Regulations, and
that the revised Recommendation ITU-R TF.460 will become effective only after the date of entry
into force established by the appropriate World Radiocommunication Conference,


1 that the World Administrative Radio Conference (Geneva, 1979) (WARC-79) has
decided that UTC shall be used in all international radiocommunication activities;

2 that according to Recommendation ITU-R TF.536 and in accordance with the
recommendation of the CGPM the designation of UTC is to be used in all languages;

3 that the UTC system with leap seconds was essentially introduced to provide a common
standard for broadcast time and frequency signals generated from the UTC(k) physical
representations and give ready access to low-precision UT1 from these broadcast times and
frequency signals maintained within the necessary approximation for celestial navigation;

4 that an increasing number of applications require traceability to a continuous
international time-scale;

5 that time references other than UTC that are proliferating do not offer the reliability,
accessibility, or metrological quality of the international reference UTC;

6 that celestial navigation is no longer a primary means of navigation;

7 that users can easily access UT1 information by means other than radio transmissions,


1 that UTC as defined in Annex 1
should be used to designate the time in all international telecommunication activities and in all
official documents of ITU;

2 that the application of leap second adjustments to UTC should cease on 1 January five
years after approval by the appropriate World Radiocommunication Conference;

3 that the UTC frequency should be used as the ultimate reference for standard-frequency

4 that the transmission of time signals should not deviate from UTC by more than
100 microseconds;

5 that the emitted standard frequencies should not deviate by more than 1 part in
1011 from the UTC frequency;

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6 that the time signals emitted from each transmitting station should bear a known relation
to the phase of the carrier,


the IERS and the service providers of Global Navigation Satellite Systems to offer convenient
access to values of UT1-UTC so that users have access to UT1.


Time and time-scales

A Universal time (UT1)

UT1 is the time determined from astronomical observations
of the rotation of the Earth with respect to the International Celestial Reference System. A technical
description and the concepts involved are available in the publications of the IERS.

B International atomic time (TAI)

The international atomic time (TAI), based on the SI second, as realized on
the rotating geoid, is formed by the BIPM on the basis of clock data supplied by cooperating
establishments. It is in the form of a continuous time, e.g. in days, hours, minutes and seconds
from the origin 1 January 1958 (adopted by the CGPM 1971). TAI is not physically realized and
consequently is not suitable for time dissemination.

C Coordinated universal time (UTC)

UTC is the time-scale maintained by the BIPM which forms the
basis of a coordinated dissemination of standard frequencies and time signals. It corresponds
exactly in rate with TAI but differs from it by an integral number of seconds.

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NOTE 1 — The value UT1-UTC, either observed or predicted, is determined by the IERS and
disseminated by multiple sources. It may increase or decrease without limit. It may be regarded as a
correction to be added to UTC to obtain UT1.

NOTE 2 — The dissemination of the previously coded values of UT1-UTC will be

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