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

[Tom Van Baak]

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
> 
> My Z3815A sees PRN 32 now albeit as unhealthy.
> 
> Bruce

Right, I concur! Here's my Z3815A output a few minutes ago:

Tracking: 7 ____   Not Tracking: 4
PRN  El  Az  C/N   PRN  El  Az
  3  46 268   41     6   6 168
  9  14  94   41    19  33 307
 14  29 183   38    26   6  33
 15  16  41   43    32  Not OK
 18  62  58   46
 21  40 113   45
 22  71 259   48

/tvb