Re: [LEAPSECS] Risks of change to UTC

From: M. Warner Losh <imp_at_BSDIMP.COM>
Date: Sat, 21 Jan 2006 00:33:21 -0700 (MST)

In message: <003a01c61e57$660af520$62c20444_at_Fnord>
            "Brian Garrett" <> writes:
: > But the protocol for broadcasting DUT1 in, e.g., WWV, does not provide
: > for DUT1 values of more than plus or minus 0.9 s. The value of DUT1
: > could be announced by voice message -- but that would not be
: > language-independent. If I travel to asia in my boat, I will not be
: > able to benefit from DUT1 announcemnts in Japanese from JJY or in
: > Chinese from BPM (or whatever their standard time and frequency station
: > is). An longwave broadcasts such as those from WWVB do not have voice
: > modulation at all!
: >
: WWVB broadcasts the DUT1 correction in binary-coded decimal form, and is
: capable of representing DUT1 values up to +/- 1.5 seconds with their current
: format. I would think other longwave stations do the same, but not knowing
: their particular BCD format I couldn't say what DUT1 values they are capable
: of representing.

Taking a long term view, some changes in the broadcast format or
interpratation would be necessary. It is quite possible to multiplex
these bits so that successive opportunities to transmit the DUT1
encode additional digits as well. This would mean it would take a
while to transmit DUT1, but such operational issues have been deemed
acceptable in systems such as GPS which transmit leap second
information only a few times an hour.

There appears to be about 13 unused bits in the WWV stream at second 8, 14,
24, 27, 28, 34, 42, 43, 44, 45, 46, 47, and 48. Granted, some of
these are spacer bits between BCD digits, but they could be reclaimed.
The WWVB timecode has fewer free
bits at 9: 5, 11, 14, 21, 24, 34, 35, 44, and 54. 10 if you count the
redundant sign bit. With enough advance notice, these bits could be
used to encode larger DUT1 values.

If you travel to asia, you will no doubt know what DUT1 is to within a
second before you leave the US. The rate of DUT1 change is on the
order of 1s per year. This should obviate the need to be told the
current DUT1 value every minute. Even the DUT1 values broadcast to
the .1s level only change monthly or so (although there are provisions
to change them with only 2 weeks notice).

I have no delusions that changing the meaning of the bits in the time
codes braodcast from WWV and WWVB will happen in less than a decade...

Received on Fri Jan 20 2006 - 23:34:19 PST

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