NorthStar Navigation Multi-Function Unit M84 - Manual (Page 34)

Northstar M121/M84 Installation and Operation Manual 33
The satellite window has information about the
GPS satellites and GPS position.
To go to the satellite window, press
DISPLAY
,
select More, then select Satellite.
The satellite window shows:
8-1 Satellite window
A Status of GPS antenna, for example
Acquiring, GPS fix, No GPS. If
the unit is in Simulate mode it displays
Simulate (see section 2-6).
B Time and date from GPS satellites. Time is
local time (UTC [GMT] plus local offset, see
section 19-4)
C HDOP: The error in the GPS position caused
by satellite geometry. A low value indicates
a more precise fix, a high value a less precise
fix
D Signal strengths of up to twelve visible GPS
satellites. The higher the bar the stronger the
signal
E Boat position
F Positions of visible GPS satellites:
Outer circle is horizon
Inner circle is 45° elevation
Centre is directly above
North is at top of window
G If the boat is moving, COG is a line from
centre
9 Sonar fishfinding: Introduction
Sonar functions require an optional sonar
transducer to be installed and set up.
This section explains how to interpret the sonar
displays, when and why to use the different
frequencies and how fish are detected and
displayed.
It also describes Gain and Range and shows
examples of some of the different sonar
displays.
9-1 Using the Instrument
The Instrument uses a sonar transducer
attached to the hull. The transducer generates
an ultrasonic pulse (sound that is above the
hearing range of the human ear), which travels
down towards the bottom at a speed of about
4800 ft/sec (1463 m/sec), spreading out into a
cone shape.
When the pulse meets an object, such as a fish
or the bottom, it is partly reflected back up
towards the boat as an echo.
The depth of the object or bottom is calculated
by the Instrument by measuring the time taken
between sending a pulse and receiving the
echo. When an echo has been returned, the
next pulse is sent.
The Instrument converts each echo into an
electronic signal, displayed as a vertical line of
pixels.
F
D
E
G
C
B
A