Therefore, every
time
you
turn the unit
on,
the settings are exactly
as you
left them.
However, you can return the UltraNav II to it's factory settings using the
preset
feature. This returns all sonar and GPS receiver settings
at the
same time. To usethis
feature, press the MENU key
sixtimes
whiJe
a sonar
screen is
showing. Next, press the
key adjacent to the "PRESET SONAR
AND GPS" label. The screen will clear and return to thesonar display.
TRANSDUCER CONE ANGLES
The sound waves from the
transducer spread out into thewater in a cone
• shaped beam, This looks much like the beam from a
flashlight
The
angle
• between the outside
edges of the cone is the cone
angle.
Eagle offers a choice of transducers with either an 8 or
20 degree
cone
angle.
The transducer
supplied
with the UltrNav II has a 20 degree cone
angle. Typically,
wide cone
angle transducers (2O degrees) are ideal for
operating in shallow to medium water
depths. The 20 degree cone
angle
allows you
to see more of the
underwater world. In 15 feet of waterthe 20
degree cone
covers
an area about six feet across. The 8 degree
trans-
ducer covers
only about a two foot circle;
The 20 degree transducer is almost always the best to use in
fresh•water,
the 8
degree
mostly in salt water. In a
deep water
envirOnment, (300 feet
-
freshwater,
1 Oofeet- salt
water) the narrowcone angle
is more desirable.
Since the sound energy
is concentrated in a smaller area, it can penetrate
to much deeper depths.
Both 8 degree and 20
degree transducers give accurate bottom
readings,
even
though
the
bottom.signal is much wider on the 20
degree model. This
is because you are seeing more of the bottom. Remember, the shallow
edge of the
signal shows you
the true
depth.
The rest of the
signal tells
you
whether
you are over rocks; mud, etc.
if the cone
passes over a
fish in shallow
water, the
signal displayed on the
UltraNav II
may
not arch at all. This is due to the narrow cone diameter and
the resolution limitations of the
display.
FISH ARCHES
Fish arches are created when the cone of sound passes over a fish. The
distance to a fish when the cone first strikes it is shown as "A" on the next
page. When the center Of the cone strikes the
fish, the distance is shorter
as shown "B" As the cone
leaves the
fish, the distance increases again as
shown in "C".
GPS
- HOW IT WORKS
The Global Positioning System (GPS) is the best approach
to navigation
that has ever been devised. Conceived by the Department of Defense
(DOD)
and the United States military,
the GPS
system is an answerto their
needs of 24 hour
global positioning, 365 days a
year.
Basically,
the
system
works b
using
a cohEtëllatibn Of sàtOllites
orbiting
Earth 11,000 miles in
space. There will be 21 satellites
in orbit when
the
system is
fully operational. Three more satellites will act as spares, for a
total of 24. When all satellites are in place, at least four
of
them
will be in
view
nearly anywhere on Earth
twenty-four hours a
day.
The OPS receiver
requires at least three satellites to
give a
"2D" fix. (A
2D fix is
your position
in
latitude/longitude.
A 3D fix is
your latitude/longitude plus
altitude.)
When
it locks on to at
least four
satellites, it displays a
3D fix.
As the receiver locks on to
each
satellite, it calculates the distance from the
satellite by measuring the length of time it takes the radio signal to reach
it. Each satellite has an extremely accurate clock that tells the receiver
when the radio transmission started. The receiver compares that time
against its own clock, thus it knows how long it took the radio signal
(travelling
atthe
speed
of
lightl)
to
reach it. If
you
knowtime and
speed,
then
you can calculate distance. Once
you have this from three
satellites,
then
the receiver can determine position.
It takes three satellites to
determine posifion.
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