B&G Network GPSplus - Manual (Page 42)

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SETTING THE ANCHOR ALARM
1. Press
the POS key.
2. Press
the SETUP key until AnCHOr AL is displayed.
3. Press the ENTER key, the display will flash the current
anchor alarm radius.
4. Use
the ▼ STEP ▲ knob to alter the value in the range
0.01 to 9.99NM.
NOTE: The value is factory set to 1.00NM. Due to
external factors this alarm may not be reliable below
0.05NM. The value will be displayed in Statute Miles or
Kilometres if those units have been selected.
5. Press
the ENTER key to memorise your setting. The
display will now flash the current alarm state.
6. Use
the ▼ STEP ▲ knob to select ON or OFF.
NOTE: The anchor alarm is factory set to OFF.
7. Press
the ENTER key to memorise your setting.
To change the alarm state without adjusting the radius, miss
out step 4.
HDOP ALARM
As in all radio navigation systems, the accuracy is affected
by the geometry of the situation. Probably the most familiar
examples of this today is the practice of avoiding "small
crossing angles" in Loran-C or Decca lines of position
(LOP). These hyperbolic systems operate with fixed site
transmitters so the angles are constant at any particular
location. GPS uses moving transmitters (satellites) and
therefore the geometry or crossing angles are constantly
changing. In 2-dimensional GPS navigation, the lines of
position are moving circles on the Earth’s surface that are,
at all points, equidistant from a satellite. The effects of
geometry on accuracy can be summarized in a single
number, called the Horizontal Dilution of Precision (HDOP).
The accuracy obtainable from a particular set of satellites is
equal to the pseudo-range measurements multiplied by the
HDOP. In order to avoid extra-ordinary errors due to short
periods of very poor geometry the GPSPlus software will not
use satellite constellations with an HDOP higher than
twelve. The HDOP alarm allows you to be alerted when the
HDOP value becomes larger than a preset value (up to 12).
SEtUP
AnCHOr AL
OFF