Spectracom - Essential Ingenuity

GPS Tracking and Low GPS Quality Alarms

Question

What can be done if Ageless Ocscillator is reporting GPS Tracking and Low GPS Quality Alarms?

Answer

Sample Alarm Log entry:

TIME= 16:24:12 DATE= 2013-11-05 STATUS CHANGE <TEMP= +40.0>
COOLING FAN= OFF
ALARM RELAYS: MAJOR= OFF MINOR= ON  
ACTIVE ALARMS: MINOR          
TRACKING ALARM 1
TIME= 16:32:23 DATE= 2013-11-05 STATUS CHANGE <TEMP= +40.0>
COOLING FAN= OFF
ALARM RELAYS: MAJOR= OFF MINOR= OFF
ACTIVE ALARMS: NONE          

Sample GPS Qualification Log entry:

DH
TIME=16:00:00 DATE=2013-11-05
 0=00000   1=00000   2=00000   3=00001   4=00026
 5=00535   6=01885   7=01095   8=00058   9=00000
10=00000  11=00000  12=00000   Q=03599

TIME=17:00:00 DATE=2013-11-05
 0=00009   1=00000   2=00004   3=00355   4=00624
 5=01122   6=01010   7=00473   8=00000   9=00000
10=00000  11=00000  12=00000   Q=03178

TIME=18:00:00 DATE=2013-11-05
 0=00000   1=00000   2=00000   3=00002   4=00088
 5=00853   6=01317   7=01139   8=00201   9=00000
10=00000  11=00000  12=00000   Q=03598

TIME=19:00:00 DATE=2013-11-05
 0=00000   1=00000   2=00000   3=00006   4=00091
 5=00834   6=01877   7=00719   8=00073   9=00000
10=00000  11=00000  12=00000   Q=03594

TIME=19:16:28 DATE=2013-11-05
 0=00000   1=00000   2=00000   3=00000   4=00052
 5=00130   6=00628   7=00174   8=00003   9=00000
10=00000  11=00000  12=00000   Q=00987



It appears from the log information these units are having GPS Reception problems.
For very short time periods the number of satellites tracked drops below the minimum allowed quantity of four satellites. This triggers the alarm but should not affect the 10 MHz signals.
They seem to have a wide range of satellites tracked over any given hour which suggests the antennas have partially blocked sky views. This can usually be remedied by moving the antenna to a place where they can see more of the overall sky. This is the best resolution.

If this is not an option you could also try setting the GPS Qualification Algorithm to allow an occasional drop in the number of satellites tracked without triggering an alarm.  By defauklt the GQA is set to 1 which requires the 8197 to constantly track four or more satellites. If you change the GQA to 3 it will require the unit to track at least 4 satellites but then afterwards will allow it to drop to tracking at least one without triggering the alarm.
To set the GQA go into to test mode (TM ON) and then type GQA 3. This will set the GQA to level 3.
 
Hopefully one of these methods will resolve your problems.
 
Reference:
 

GPS Qualifiying Algorithm (GQA)

                GQA1  -four qualified satellites  required at all times (Default mode)
                GQA2 – Only one satellite required.  No 3-D fix required. 
                GQA3 – Only one satellite after 3-D fix for one minute. 
                     
                 Older units needed PHO turned off prior to changing the GQA to higher number (Two step process).
 
GQA 3 with a Current level of 1 (then 2)
There are three GQA levels.   GQA 1, 2 and 3.  GQA 1 indicates that you have to always track at least four qualified satellites (factory default) while GQA 2 says that you only need to ever track just one qualified satellite.    GQA 3 is a combination of both 1 and 2.  GQA 3 indicates that you have to initially have four qualified satellites for a period of time, but then it can drop to just one satellite.  GQA 2 is not a recommended setting to use as it is recommended to have at least four satellites to obtain a 3-d fix first before dropping to just one satellite. 
 
When in GQA 3, the Current Level starts at GQA 1 while it is requiring four satellites to obtain a 3-D fix.  Once the GPS receiver has achieved a 3-D fix for 60 seconds, the Current Level with then switch to 2, indicating that it has met the minimum requirements of a 3-D fix for 60 seconds and so it now only needs one qualified satellite to maintain lock.  It won’t ever progress to a level of 3 because GQA 3 is not an individual level with its own defined rules–it’s just a combination of GQA 1 and 2.   If the GQA response shows level 2, all of the minimum GPS requirements have been met

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