ing to insure that
they see all
the underwater detail as well as
fish.
NOISE SUPPRESS
CONTROL
The noise suppress
control knob
can be used to cut down or
eliminate false flashes on the
dial. These false flashes can be
caused by ignition interference
from the boat's motor or by air
bubbles passing over the face of
the transducet
Ilirning
the knob clockwise in-
creass the amount of noise sup-
press. Always use as little noise
suppress as possible, because an
increase in it cuts down on the
ability
of the unit to show sepa-
rate signals or objects (such as
fish) close together.
Increasing noise suppress does
not affect the
sensitivity of the
unit.
RANGE
The range control is used to
select either the 0-60' or the
0-60
fathom (360')
scale. The
Noise Suppress control knob is
used to change the scales. By
pulling the
knob
out, the 0-60
fathom range is selected, and
pushing the knob in switches the
scale to the 60' range. With the
control in the 60' position,
the
range should be read on the
outside 0-60 scale. With the
control in the 60 fathom
position,
the range may be read
in fathoms on the outside 0-60
scale,
or may
be read in feet on
the inside 0-360' scale on the
faceplate.

HOW TO USE YOUR

EAGLE DEPTH

SOUNIJER

The word 'Sonar" is an abbrevi-
ation of
Sound, Navigation, and
Ranging. It was developed dur-
ing World War II as a means of
tracking enemy submarines.
Sound travels at approximately
4,800
feet
per second
through
water as compared
to approxi-
mately 1,100 feet per second
through
air.
The way a sonar works in its
simplest form is an electrical
pulse is converted into a sound
wave by the transducer and
transmitted into the water.
When this wave strikes an ob-
ject, it rebounds. Since the speed
of sound through water is
known, the time lapse between
the transmitted
signal and the
received echo can be measured
and the distance to the object
determined.
Some
fish, including
bass, catfish, walleyes,
and crappies,
occa-
sionally lie right on
the bottom. Even here
the EAGLE will show
them as you pass over,
provided
the bottom is
smooth sand, shell, or
gravel. Figure 16
shows a hard bottom
with the sensitivity
control adjusted
so

that a strong bottom

signal
is displayed
with two fish at 20
and 21 feet. A second
echo may
be displayed

that is twice as deep

as the actual bottom
signal
when the sen-
sitivity
control is
turned up high enough
to see fish.
This is caused by
the sound waves re-
flecting from the bot-
tom, bounce back from
the water's
surface, re-
turn to the bottom and
reflect back to the
sonar unit. Many
fishermen prefer to
run the sensitivity
control very high with
the second bottom
sig-
nal showing
to insure
that they see all the
underwater details as
well as fish.
The second echo is
shown at 50 feet in
figure 16.
7 12
HARD CLAY, SAND, GRAVEL, SHELL BOTTOMS
PRINCIPLE OF SONAR
flfl)))flfl)flflfl)))fl
.( (((( (((( ( ((( ( (( ( ( ((((((K
SIGNAL SENT BY LOCATOR BOUNCES BACK FROM
TARGET. TIME LAPSE INDICATES DISTANCE TO TARGET
Fig. 11
Sand bottom
Fig. 16
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