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

[Bruce Griffiths]

Magnus Danielson wrote:

> > Bruce,
> >
> >   
>   
>> >> Although it is labelled as SV number, my version of the documentation
>> >> clearly states that the meaning of byte 4 is the SV PRN#.
>> >>     
>>     
> >
> > 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#.

>> >> However as you say since the PRN# is given in the common 4 byte header
>> >> this would seem somewhat redundant.
>> >>     
>>     
> >
> > With the above writing, you can almost assume it is a documenation miss, but it
> > needs to be confirmed.
> >
> > If you look at the Item numbers, they match what is in the ICD-200 so it is
> > likely they have propper meanings.
> >
> > Also notice how the PRN number field is limited in the range 1-32 where as no
> > such limitation is given for the SV number.
> >
> >   
>   
>> >> The documentation is certainly inconsistent and confusing.
>> >>     
>>     
> >
> > Inconsistent and confusing yes, but there is only 4 characters too much that
> > cause that confusion. If you assume they should not be there it makes
> > perfectly sense.
> >
> >   
>   
>> >> I guess the operational test is:
>> >> Does the displayed SV number contain values greater than 32 (current
>> >> values for SVN can be as high as 61, the maximum value for PRN is 32)?
>> >> If so then its very likely to be the SVN and not the PRN.
>> >>     
>>     
> >
> > Rather, when dumping this, we can verify that the PRN numbers in byte 2
> > and SV number in byte 4 matches the PRN and SVN mapping available.
> > To help confuse things, I noticed that there is still birds having the same
> > PRN and SVN numbers.
> >
> > Cheers,
> > Magnus
> >
> >   
>   
Hej Magnus

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).

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).

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?

Bruce