Symmetricom Z3801A, User Manual

Page: 65 / 98

Chapter 3 Using the Receiver Status Screen
The Receiver Status Screen at a Glance
User Guide 3-21
ACQUISITION
r
ceiver Status ----------------------------
[ Outputs Valid/Reduced Accuracy ] .........
.........................
.....................................
9
UTC
ANT DLY
MODE
AVG LAT
AVG LON
AVG HGT
+1.296 us]
n Pwr: OK OCXO: OK EFC: OK GPS Rcv: OK
[ OK ]
Time
GPS 1PPS Synchronized to UTC
Position
Reference Outputs
3 2
1.000 us
[ GPS 1PPS Valid ]
03:11:57 31 Jan 1996
120 ns
Survey: 26.1% complete
N
W 37:19:31.797
121:59:52.018
60.52 m (MSL)
track
TFOM FFOM
HOLD THR
1PPS TI --
Predict 55.8 us/initial 24 hrs
Holdover Uncertainty
n: 1m 45s Present 1.0 us
RN El Az
9
Suspended: track <4 sats
Not OK
ACQUISITION profiles the process of acquiring precise time from
GPS. GPS provides time-of-day information and a 1PPS reference
signal used to discipline the internal oscillator.
Coordinated Universal Time UTC
UTC with local time zone offset LOCAL
GPS Time, with time zone offset.
LOCL GPS
Satellites currently tracked by the receiver. Four or more satellites
must be tracked to determine position. Timing information is
derived from all tracked satellites, and is considered accurate while
tracking at least one satellite from a known position. The receiver
selects satellites highest in the sky that are at or above the minimum
elevation angle specified by
ELEV MASK .
Satellites considered for tracking. These satellites are predicted to
be visible or are selected by the "sky search" algorithm. Visibility is
predicted from the satellite almanac, current time and position.
Tracking and Not Tracking tables provide supplemental information
about satellite position, signal strength and health:
PRN Identification number (pseudorandom noise code)
assigned to the satellite. Satellites are sorted by
ascending PRNs.
EI Elevation of the satellite (degrees) predicted by the
almanac. "---" denotes it is unknown, such as when
the satellite is not predicted to be visible but is selected
for tracking by the sky search algorithm.
Az Azimuth of the satellite (degrees), referenced to true
north, predicted by the almanac; "---" if unknown.
SS Relative signal strength, proportional to the signal-to-
noise ratio of the received signal. The maximum value
is 255; 20 to 30 is the minimum range for stable tracking.
Acq
Locking code and carrier tracking loops to initially
acquire the satellite signal.
Acq .
Demodulating the satellite broadcast (NAV) message,
and determining current time.
Acq ..
Reading the satellite ephemeris (orbital information)
from the NAV message.
Ignore
The satellite is excluded from the selection process.
Not OK GPS or Time RAIM reports the satellite is unhealthy.
Time
Time of day:
Position
An accurate position is necessary to transfer time from GPS.
Two position
MODE s are provided, hold and survey.
In
Hold
mode, a fixed position is used to derive time. This position
may be specified if known, or determined by the survey process.
In
Survey
mode, position is determined from GPS. Four or more
satellites must be tracked. Successive positional estimates
(pseudoranges) are refined to obtain the true position, which is
entered as the held position at the completion of this process.
Averaged (
AVG
) position coordinates and progress are reported
while surveying. When surveying is suspended, an advisory
message describes the reason:
Suspended
:
track
<
4 sats
Four or more satellites must be tracked to determine position
Suspended
:
poor geometry
DOP (dilution of precision) is too large for an accurate pseudo-
range measurement.
Specifying an approximate initial (
INIT
) position will reduce
satellite acquisition time.
GPS Time
GPS
[ ? ] identifies a default power-up setting that is corrected when the
first satellite is tracked.
+1
(or
-1
)
leap second pending
is reported if a leap second
correction to UTC is pending.
GPS 1PPS indicates the validity of the GPS 1PPS reference:
Synchronized to UTC (or GPS Time )
1PPS reference is synchronous with GPS
Assessing stability...
1PPS must be accurate for 35 seconds
Inaccurate: not tracking
One or more satellites must be tracked
Inaccurate: inacc position
Postition must be known to derive time
Inaccurate: Time RAIM err
GPS timing integrity is suspect.
ANT DLY offsets the GPS 1PPS reference to compensate for
signal propagation delays introduced by the antenna system.
(Time is referenced to the position of the antenna.)
Tracking
Not Tracking
Questionable accuracy...