[time-nuts] NAVSTAR proteus GPS time and frequency unit

Chuck Harris cfharris at erols.com
Mon Nov 9 23:37:38 EST 2015


Thanks for the detailed reply.  I haven't had a need (read: no customer
has paid me to do so...) to wallow through the GPS ICD, so that document
is foreign to me.

Your explanation clarifies the situation...  Now it makes sense.


-Chuck Harris

Magnus Danielson wrote:
> Chuck,
> Because all the leap-second info is kept in GPS-calender form, and essentially
> indicating current leap-second difference and which GPS week (modulo 256). Check out
> the ICD for yourself, IS-GPS-200H:
> 8<---
> Coordinated Universal Time (UTC).
> Page 18 of subframe 4 includes: (1) the parameters needed to relate GPS time to UTC,
> and (2) notice to the user regarding the scheduled future or recent past (relative to
> NAV message upload) value of the delta time due to leap seconds (ΔtLSF), together
> with the week number (WNLSF) and the day number (DN) at the end of which the leap
> second becomes effective. "Day one" is the first day relative to the end/start of
> week and the WNLSF value consists of eight bits which shall be a modulo 256 binary
> representation of the GPS week number (see paragraph 6.2.4) to which the DN is
> referenced. The user must account for the truncated nature of this parameter as well
> as truncation of WN, WNt, and WNLSF due to rollover of full week number (see
> paragraph 3.3.4(b)). The CS shall manage these parameters such that, when ΔtLS and
> ΔtLSF differ, the absolute value of the difference between the untruncated WN and
> WNLSF values shall not exceed 127.
> Depending upon the relationship of the effectivity date to the user's current GPS


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