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 _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
