[time-nuts] GPS PRN vs SV...??

[Magnus Danielson]

From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Subject: Re: [time-nuts] GPS PRN vs SV...??
Date: Sat, 09 Feb 2008 21:57:57 +1300
Message-ID: <47AD6B15.7090701 at xtra.co.nz>

Hej Bruce,

> > > It actually does not clearly states that in my documentation. It
> > > contradicts itself!
> > >
> > > Byte Item      Type   Value	Meaning
> > > 2    Sat PRN # UINT8  0		Data that is not satellite ID-specific
> > > 		      1 to 32	Satellite PRN number
> > >
> > > Byte Item      Type   Meaning
> > > 4    SV number UINT8  SV PRN number
> > >
> > > The field SV number (which is what we are looking for) is said to have the
> > > meaning of SV PRN number.
> > >
> > >   
> >   
> Perhaps Trimble's SV number = GPS SVID (as defined on page 8 of the GPS
> Interface control document)
> for SVs:  SVID = PRN#.

Yes, but SVID isn't SVN, which may be the cause of confusion.

Actual SVNs isn't meaningfull for normal GPS users and bears no meaning to the
receivers, where SVID and PRN# is the important things.

> Perhaps all is explained, if one notes that the SVID's described in the
> GPS Interface Control document are identical to the SV PRN# except when
> SVID is used to differentiate between data pages.
> PRN# can be as high as 37 (but not for SVs which are limited to a
> maximum of 32).

It would appear that during normal operation PRN# is set to the SVID. There is
actually a SVID to PRN# mapping provided, but the SVID range isn't free enought
to hold SVN numbers.

> I didnt find any mention of the SVN # in the Interface Control document
> so maybe it isnt broadcast (or at least it isnt publicly available via
> GPS messages).

Looking into IS-GPS-200D I am inclined to agree.

> The Motorola M12+ user manual  indicates that the SVID is used in some
> messages.
> 
> Has anyone dumped Thunderbolt report packets 0x58 to a text file?

Requesting data for PRN# 1-32 and hex-dumping the result would be of
interest.

Cheers,
Magnus