[time-nuts] Trimble Nortel GPSTM Boards

Bob Camp lists at rtty.us
Thu Aug 1 10:31:17 UTC 2013


Hi

You may have your elevation mask set to low for your antenna or a multi path issue from some other source.  If the survey location is good to under a meter and the signals are good, there should be very little shift as sats are picked up or dropped. 

Bob

On Aug 1, 2013, at 5:09 AM, GandalfG8 at aol.com wrote:

> 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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