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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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