Properly designating UTC time

Discussion in 'Ham Radio Discussions' started by N7BKV, Jun 10, 2019.

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  1. KT1F

    KT1F Ham Member QRZ Page

    Or any other timezone. It doesn't need to be UTC, so long as the sender and receiver understand each other through prior agreement or whatever. That was my point but we're arguing semantics.
  2. KA9Q

    KA9Q Ham Member QRZ Page

    It used to be much worse. UTC officially began on January 1, 1960. Until 1972, WWV ran small frequency offsets and also made small step adjustments in time, all to track earth rotational time. Throughout the 1960s, the frequency offset was -15 or -30 ppb with occasional timing jumps of 100, 50 or even 5 milliseconds, all on an ad-hoc basis. In 1965 there were four changes in frequency and/or time. On January 1, 1972 at 00:00:00, an ad-hoc jump of +107,758 microseconds was added to put UTC exactly 10 seconds behind TAI (international atomic time), the frequency offset was permanently set to zero, and the modern practice of inserting leap seconds every 6 or 12 months began.

    This keeps the TAI-UTC offset equal to an integer number of seconds. Right now, TAI is exactly 37 seconds ahead of UTC, but this will change with the next leap second. Because neither TAI nor GPS follows leap seconds, and GPS time started on Sun 6 Jan 1980 when UTC had had 9 leap seconds since 1972, GPS is currently 18 seconds ahead of UTC. GPS is always 19 seconds behind TAI.

    Simple, huh?

    It would be if everything just used one of the atomic time scales (any atomic time scale) internally. The only hassle comes when converting to legal time (i.e., UTC) for display to humans. I know all this stuff because I actually wrote software to do it for times back to January 1, 1958, the nominal start of TAI (though UTC didn't become official until 1960).
    Last edited: Jun 17, 2019
    K5ABB likes this.

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