[time-nuts] SVN-32

Magnus Danielson magnus at rubidium.dyndns.org
Fri Mar 7 18:43:41 EST 2008


From: mikes at flatsurface.com (Mike S)
Subject: Re: [time-nuts] SVN-32
Date: Fri, 07 Mar 2008 18:17:03 -0500
Message-ID: <20080307231705.49A361165C3 at hamburg.alientech.net>

> At 05:04 PM 3/7/2008, Bruce Lanning wrote...
> >Those interested in the subject satellite should check the below 
> >page...
> >
> >http://groups.google.com/group/alt.satellite.gps/browse_thread/thread/d9ecefc77d23328e/fe7f019259416b60
> 
> That article was already cited here, and has a lot of inaccuracies.
> 
> 1) SVN32/PRN32 was previously operational, and healthy, from 11 
> December 1992 until 28 January 1993, when its PRN was changed to 1.
> 
> 2) GPS has "always," and only, been defined for PRN numbers 1-32. There 
> has never been a PRN 0. (see Table 3-I in 
> http://www.navcen.uscg.gov/pubs/gps/icd200/ICD200Cw1234.pdf )

Even in the comments they have trouble to correctly interprent the ICD 200
document.

They miss that the almenac data has dedicated slot for PRN1 to PRN32. A GPS
that fails due to PRN32 is prepared fro PRN30 and PRN31 too... in parts at
least, so specific bugs further down the line is to be expected.

> Apparently, some early military GPS receiver(s?) had software which 
> incorrectly used zero based indexing for PRNs (i.e. 0-31 instead of 
> 1-32), and so had problems with PRN32. That's why SVN32 was changed 
> from PRN32 to PRN1 after being on for only a few weeks. 

See this memorandum:
http://www.navcen.uscg.gov/gps/geninfo/50SW_GPSW_letter.pdf

The PLGR and MAGR has this problem.

You can implement PRN32 as PRN0 internally if you so wishes. As long as the
mapping is correct all the way.

The US Coast Guard have now sent out a warning on the GPS receiver issue:
http://www.navcen.uscg.gov/lnm/Saab_R3_AIS_prob.htm

SAAB have an updated list of messages here:
http://www.saabgroup.com/en/AboutSaab/Organisation/SaabTransponderTech/News

Some form of software upgrade is underway.

Cheers,
Magnus



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