[time-nuts] Trimble Nortel GPSTM Boards

[GandalfG8 at aol.com]

Hi Charles
 
Thanks for your comments, the surveyed position on this is looking pretty  
good but what I have now realised is that the severity of the jumps  seems 
very much related to the number of sattelites being tracked.
 
Switching from 8 to 7, or 7 to 8, sats seems to produce the biggest  step 
change whilst switching in either direction between 5 and 6, for  example, 
doesn't seem to show up at all on the monitored DAC voltage.
Ok, I take that back, it does still seem to depend on the number of sats  
being switched between but I've just seen a switch from 5 to 4 sats induce a  
very noticeable step change in DAC voltage, so the relationship  doesn't 
appear to be linear.
 
Unfortunately I need to power this down now for a few days but  will 
investigate more later.
 
Regards
 
Nigel
GM8PZR
 
 
In a message dated 01/08/2013 09:45:24 GMT Daylight Time,  
charles_steinmetz at lavabit.com writes:

Nigel  wrote:

>at times I'm seeing very noticeable step changes in the DAC  voltage 
>on this one as that happens.
>       *   *   *
>I am a bit surprised by the extent, a  Mark Sims online plot from 
>2012 shows some correlation on an NTGS50AA  but not as noticeable as 
>this, and I  don't recall seeing  anything quite so pronounced on a 
Thunderbolt.

IME (with TBolts), the  magnitude of the DAC steps with constellation 
changes varies with the  accuracy of the positional data used by the 
GPS.  To a point, the  more accurate the survey, the smaller the DAC 
jumps will be.  (Other  errors prevent reducing the 
constellation-change DAC steps to  zero.)

Mark has commented here on survey accuracy, and the methods he  used 
in Lady Heather to maximize it.

Best  regards,

Charles




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