Symmetricom Z3801A, User Manual

Page: 49 / 98

Chapter 3 Using the Receiver Status Screen
Using and Reading the Receiver Status Screen
User Guide 3-5
An accurate position is necessary to derive precise time from GPS. The
Position quadrant indicates that the Receiver is in survey mode, which
uses GPS to determine the position of the GPS antenna. This process
has not yet started, since position calculations can be performed only
while tracking four or more satellites. INIT LAT, INIT LON, and INIT
HGT are the initial estimate of the true position. These coordinates are
refined by the survey process. The Receiver uses this position and the
time-of-day to select satellites to track. Therefore, you can reduce
satellite acquisition time by specifying an close approximation of
position and time.
Now, let’s send the :SYSTEM:STATUS? query again to see what kind
of progress the Receiver has made.
You can now see that the Receiver is tracking several satellites as
shown in Figure 3-2. The process of acquiring and tracking satellites is
described in the following paragraphs.
Figure 3-2. Receiver Status Screen Displaying Initial Satellite
Acquisition
SYNCHRONIZATION
Receiver Status
---------------------------- ----------------------------
[ Outputs Valid/Reduced Accuracy ] ...........................
................................................
......................................................
ACQUISITION
ELEV MASK
Not Tracking: 4
Locked to GPS: stabilizing frequency
UTC
ANT DLY
MODE
AVG LAT
AVG LON
AVG HGT
HEALTH MONITOR
PRN
Recovery
Holdover
Power-up
SmartClock Mode
Satellite Status
Tracking: 5
Self Test: OK Int Pwr: OK Oven Pwr: OK OCXO: OK EFC: OK GPS Rcv: OK
[ OK ]
Time
GPS 1PPS Synchronized to UTC
Position
Reference Outputs
PRN El Az
2
7
15
19
22
SS
134
117
54
29
128
El
70
46
33
28
65 9 11 292
16 24 243
10 deg
6 1
1.000 us
+71 ns relative to GPS
[GPS 1PPS Valid]
17:56:44 31 Jan 1996
0 ns
Survey: 1.2% complete
N
W
37:19:34.746
121:59:50.502
+34.14 m (MSL)
>>
Az
337
188
82
113
91
*26 Acq..
31 -- ---
*attempting to track
TFOM FFOM
HOLD THR
1PPS TI
Predict --
Holdover Uncertainty