[teqc] poor tracking of L1 with NetRS and constant value of MP1 (0, 15)

Jeff Freymueller jeff.freymueller at gi.alaska.edu
Fri Jan 16 12:21:14 MST 2009


Is the position solution normal, given the data that were recorded,  
and are the phase residuals normal?

Can you rule out a significant accumulation of snow or ice on the  
antenna, or some obstruction like heavy vegetation? (I doubt the  
obstruction explanation, given that it is winter, but it could explain  
the poor tracking). I would also check the L1 SNR to see if it is  
normal (compared to your earlier data). I would guess that the L1 SNR  
is low, in addition to L2 being very low or too low for continuous  
tracking. If it is not snow, ice or an obstruction, then I would bet  
you have a hardware problem that will require replacing the antenna,  
cable, or receiver.

The PBO site AV37 started to behave in a similar way to what you have  
described back in mid-September, just a few weeks after it was  
installed. The cause of that problem is not known, because they have  
not yet visited the site. In any case, I don't think the problem is  


On Jan 16, 2009, at 10:05 AM, Lou Estey wrote:

> Dear Giorgi,
>> Perhaps you have encountered something similar in the past:
>> We have installed a Trimble NetRS receiver as a permanent station  
>> at Cabo Busto (Asturuas, Spain). One Hjek the station was working  
>> fine, but afterwards it started to have problems tracking the L1  
>> signal.
>> SV 
>> + 
>> | 
>> --------| 
>> --------|--------|--------|--------|--------|--------|--------+SV
>> 22|Lcccccccccccc            
>> LLccccLooooooccc.                              | 22
>> 12| 
>> LccIooooooooooooocccLL 
>>                                                 .| 12
> The 'c' (on these lines and for the other GPS SVs) indicates a  
> problem with tracking
> L2, not L1; 'c' means 'no A/S; L1 C/A', i.e. the rx _is_ tracking L1  
> (and only
> L1) for both phase and code pseudorange during those times.  It  
> looks like the
> L2 tracking is a problem mostly at lower elevations.
> Have you tried an antenna swap?
> --lou
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Louis H. Estey, Ph.D.              office:  [+001] 303-381-7456
> UNAVCO, 6350 Nautilus Drive           FAX:  [+001] 303-381-7451
> Boulder, CO  80301-5554            e-mail:  lou  unavco.org
>   WWW:  http://www.unavco.org   http://jules.unavco.org
> "If the universe is the answer, what is the question?"
>                                               -- Leon Lederman
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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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:   907-378-7556
Fairbanks, AK 99775-7320           email: jeff.freymueller at gi.alaska.edu
URL: http://www.gps.alaska.edu/jeff/jeff.html

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