[time-nuts] PP2S

Dennis Ferguson dennis.c.ferguson at gmail.com
Sun Sep 16 21:42:44 UTC 2012


On 16 Sep, 2012, at 17:11 , Tom Van Baak wrote:
> Some GPSDO have both a 1PPS and a PP2S (pulse per 2 second) output. I have two questions for one of you telecom experts: 1) What is the history, and the purpose of that PP2S signal? 2) What is the official spec for which second the PP2S lands on? Is it odd seconds or even seconds? Is it GPS time (easy) or UTC (problematic)? If UTC, what happens after a leap second?

The PP2S signal is a US CDMA (i.e. CDMA2000) thing.  It is aligned
to the even seconds in GPS time.  My memory is dim but I think that
the choice relates to the fact that the CDMA spreading code LFSR
rolls over every 26.666 ms (it is a 15 bit LFSR, so dividing 32767
by 26.666 ms should be the 1.228 MHz chip rate), so it rolls over
75 times every 2 seconds.  The goal is to align the code sequence
transmitted by every station, and a 1 PPS timing reference wouldn't
guarantee that since 1 second isn't an integral multiple of the
roll over time.

Dennis Ferguson


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