BendixKing SKYMAP IIIC - Manual (Page 49)

DETAILED OPERATION
Other information that is displayed on this Screen includes:
DOP (Dilution of Precision), This is a number between 00.0 and 99.0 that represents the
dilution of quality of the calculated fix due to satellite geometry. 00.0 is best, 99.9 is worst.
If this figure is greater than 5.0, performance of the system is likely to be degraded
because some of the visible satellites appear too close to each other. DOP is calculated
from the angular separation between the various visible satellites. Greater separation
results in better fix geometry and a lower DOP. (This DOP figure is not measured in any
specific units.)
UTC/DATE, which is Universal or Greenwich Mean Time and Date.
LOCAL OFFSET, which is the difference between UTC and local time.
LOCAL TIME, which is calculated by adding Local Offset to UTC.
LAST FIX. If the unit does not have a current valid fix, this is the position at which it last
had a fix. If the unit has a fix, this is the present position.
SATS (eight or twelve satellite numbers depending model), SIGS (signal strength for each
satellite) and STAT (status of each satellite).
Each satellite has a PRN (Pseudo Random Noise) or identification number. The satellite
PRN numbers are displayed in a line beside the word SATS. The two-digit number under
each PRN number is an indication of the signal strength being received from that satellite
expressed in terms of a percentage. Best is 99, worst is 00. These numbers can be used
for finding and eliminating electrical interference. Readings of 60 and above indicate a
good installation.
DETAILE
D
OPE
RATION
Under each signal strength number is a two-character code. These indicate the status of
each satellite. These codes are: CS, CA, AS, FA, BD, MD, TA, EA, and AP. These relate
to the eight possible receiver modes and are detailed below.
CS: Code Search. This is the receiver's initial stage in acquiring a satellite. It means that
the receiver is trying to match its internal code to the satellite signal.
CA: Code Acquire. This means the satellite code has been received and matched to the
receiver-generated code.
AS: AGC Set. This means the satellite strength has been assessed and the Automatic
Gain Control has been set.
FA: Frequency Acquire. This means the receiver has correctly locked onto the satellite
data frequency.
BD: Bit Sync Detect. This means the receiver is synchronised with the satellite's data bit
stream.
MD: Message Detect. This means the receiver is synchronised with the satellite's
message stream.
TA: Time Available. This means the satellite is fully locked in and has sent down UTC
time and date information to the receiver.
EA: Ephemeris Acquire. This means the receiver is reading the constellation health
status message from the satellite. This usually takes around two minutes and is a function
that is performed in the background even if the receiver has a fix.
AP: Available for Position. This means the satellite is fully locked in and tested and can
be used for calculating position. A minimum of three satellites are necessary for a 2D fix.
Rev 9 Jul 2006 3-6 Skymap/Tracker IIIC Pilot's Guide