[teqc] dumb clock questions

Jeff Freymueller jfreymue at gi.alaska.edu
Tue Sep 6 12:35:29 MDT 2005


The clock offset values (last column) in this example make me give a 
lot of weight to Geoff's explanation for this phenomenon. The clock 
drift rate appears to be about 0.00000229 sec per second. By my 
calculation, the receiver's clock offset reached 0.5 second less than 
0.1 sec before the measurement was to be output (I estimate about 0.07 
sec before if clock drift is constant). So it is possible that the 
receiver was in the process of making some adjustment when the 
measurement was output.

If this explanation is correct, then epochs like this should be much 
more common in high rate data. In fact, the fraction of 1 msec 
adjustments that show this pattern should be roughly proportional to 
both the clock drift rate and inversely proportional to the sampling 
rate. This makes a testable hypothesis even if we don't hear from 
Trimble about it.

Jeff

On Sep 1, 2005, at 9:12 AM, Lou Estey wrote:

> As a reminder to other on the list, here are 15-sec epochs from an R7 
> exhibiting
> the ".9990000" epoch cases, with the receiver clock offset value (in 
> seconds)
> at the end of the line:
>
>   05  8 18  9 57 15.0000000  0  8G10G 3G23G 8G28G19G13G27             
> 0.000493299
>   05  8 18  9 57 30.0000000  0  8G10G 3G23G 8G28G19G13G27             
> 0.000496731
>      (rx millisecond clock reset occurs)
>   05  8 18  9 57 44.9990000  0  8G10G 3G23G 8G28G19G13G27            
> -0.000499836
>   05  8 18  9 58  0.0000000  0  8G10G 3G23G 8G28G19G13G27            
> -0.000496405
>   05  8 18  9 58 15.0000000  0  8G10G 3G23G 8G28G19G13G27            
> -0.000492971
>

Dr. Jeffrey T. Freymueller         Office: 907-474-7286
Geophysical Institute              Fax:    907-474-7290
University of Alaska, Fairbanks    Home:   907-479-3550
PO Box 757320                      Cell:   907-322-7632
Fairbanks, AK 99775-7320           email: jeff at giseis.alaska.edu
URL: http://www.gps.alaska.edu/jeff/jeff.html

Download Alaska GPS data: ftp://gps.alaska.edu/pub/gpsdata/
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