[time-nuts] SVN32 and GPS receivers, 32-bit limitations

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Feb 9 19:27:59 EST 2008


Tom Van Baak wrote:
> SatId 20959 GPS SVN32 should now be visible here in Seattle
> but I have no success seeing it with either a Thunderbolt, an
> Oncore VP, a Datum 2000, or an M12. True, the satellite is
> marked unhealthy so it is expected not to see it in the GUI or
> the timing solution.
>
> However, I am also logging raw Motorola binary messages out of
> the M12, including the @@Ha status message which reports
> unhealthy as well as healthy satellites, I think. Still no SVN 32.
>
> I have a hunch.
>
> The M12 has a @@Am message to manage the "satellite ignore
> list". According to the manual this is a 4-byte (32-bit) field and
> thus it appears there is no way to set the ignore bit for any satellite
> with SVN > 31. Perhaps not a problem. But it suggests there may
> be internal 32-bit limitations, yes?
>
> Same thing for a Thunderbolt. There are a number of places in
> the TSIP user manual that talk about 32 SVN (i.e., 0 to 31, or
> 1 to 32) and no more. A similar 32-bit binary limitation as the
> M12, perhaps?
>
> I wonder if someone at Trimble or ex-Motorola could comment.
>
> My rash prediction is that no one is going to see SVN32 with
> an Oncore VP, M12, Thunderbolt, and maybe a few others.
>
> Then again, I wonder if things might magically improve in a
> week when they set it healthy.
>
> Note this is not a operational or performance problem, really.
> GPSDO did just fine before 32 SV and a receiver overlooking
> one or two high-numbered SV due a 32-bit receiver limitation
> isn't going to make a noticeable difference in the performance
> of a multichannel receiver or GPSDO.
>
>   
Tom

What about the Trimble Resolution-T?

Its TSIP Command packet 0x39 allows for PRN values of 1-32 with 0 used
to indicate all satellites.
This range for PRN 0, 1-32 is consistent throughout the Resolution T
documentation.

Bruce



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