In message: <304A1B32-9BF5-4835-B3CA-70DAF713338D_at_semantic.org>
Ashley Yakeley <ashley_at_SEMANTIC.ORG> writes:
: On Jan 2, 2007, at 11:40, Warner Losh wrote:
:
: > The second technical problem is that the length of a second is
: > implicitly encoded in the carrier for many of the longwave time
: > distribution stations. 10MHz is at SI seconds. For rubber seconds,
: > the broadcast would drift into adjacent bands reserved for other
: > things.
:
: At 1000ns, the carrier would drift by 10Hz. Surely the bandwidth is
: big enough for that?
Likely. I hasn't done the math. I didn't know if the rubber seconds
idea was only on leapday, or for the whole year.
: > Also, GPS would have to remain in SI seconds. The error in GPS time
: > translates directly to an error in position. Approximately 1m/ns of
: > error (give of take a factor of 3). Rubber seconds would require that
: > the rubber timescale be off by as much as .5s. So GPS has to remain
: > in GPS time (UTC w/o leap seconds, basically). That means that the
: > rubberness of the seconds would need to be broadcast in the
: > datastream.
:
: GPS is TAI. I'm not proposing abandoning TAI for those applications
: that need it.
GPS is also used for UTC today. Many ntpd's are stratum 1 tied to a
GPS receiver. ntpd is UTC, by definition.
The gymnastic necessary to produce UTC timing signals from GPS
(non-rubber) timing signals with rubber UTC secods would be, ummm,
very interesting.
Warner
Received on Tue Jan 02 2007 - 12:49:18 PST