[Thumbgps-devel] [gpsd-dev] PPS over USB

[Ron Frazier (NTP)]

Hi all,

Gary said his posts are bouncing, and to please post this to the list.  
So, this post serves that purpose, as well as being my reply.

Thanks for the note Gary.  I guess you're right, as long as PPS is in 
control.  I presume you could still get the numeric value for the second 
from NMEA and start time for it from the PPS.

Check what return address shows up when you send a message to 
thumbgps-devel and make sure it matches what you signed up with.  You 
may have to put a custom identity in your email, like I did with my 
return address above, to get it to accept your posts.

Sincerely,

Ron


On 5/2/2012 3:42 PM, Gary E. Miller wrote:
> Yo Ron!
>
> On Wed, 02 May 2012 09:40:41 -0400
> "Ron Frazier (NTP)"<timekeepingntplist at techstarship.com>  wrote:
>
>    
>> Just wondering.  On the USB + PPS + PL2303 concept, has the long term
>> variation that has been observed in NMEA data in other similar units
>> without PPS been accounted for?
>>      
> Of course, it is an unavoidable side effect of the variable length NMEA
> protocol and the variable time for the GPS to compute depending on
> satellite configuration.
>
>    
>>   I have personally observed a
>> variation in NMEA data on my Globalsat Sirf III USB device of up to
>> +/- 70 ms over several days.
>>      
> Yup, sounds right.  If you look closely, the time jump is when the
> number of sats used in the cmopuatation changes.
>
>    
>>   Will having the PPS coming though USB
>> solve that problem?
>>      
> Nope.  NMEA is NMEA and PPS is PPS and they are not related except
> to the partial second.  So the NMEA jitter will still be there, but who
> cares when the PPS is stable to 0.5 milliSec.
>
> BTW, for some reason thumbgps-devel rejects my posts, so pass this on
> to the list.
>
> RGDS
> GARY
> ---------------------------------------------------------------------------
> Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
> 	gem at rellim.com  Tel:+1(541)382-8588
>    


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Ron Frazier
timekeepingdude AT techstarship.com