The sensitivity con-
trol on
your EAGLE
might
be compared
to
the volume on a radio.
Thrn the sensitivity
knob to the right and
you increase the re-
ceiver sensitivity; turn
it to the left and you
reduce it. This feature
is provided so that you
can use your EAGLE
over both deep and
shallow water and you
should
always adjust
the gain so that a
bright
bottom
signal
shows on the dial, re-
gardless of depth. Jf
you fail to do so and
have only a faint bot-
tom signal the dial
will fail to show fish
in the water between
the transducer and the
bottom. This condition
is shown in the draw-
ing above — the
fish
are there but they
aren't shown on the
dial because the gain
is set too low.
The Eagle depth sounder
trans-
mits a high frequency
sound
wave (which is inaudible to fish
as well as humans) through
the
watet At the same time, a high
intensity neon bulb whirls at a
constant speed
behind the dial
on a disc driven by an accurately
governed
motor. The bulb is
lighted every time the transmit-
ter fires. This provides
a visual
reference
point on
the dial which
is used as a starting point to
measure depth, and as an indi-
cator that the depth sounder is
on. Even though the neon bulb
flashes, it happens so often that
the human
eye sees it as a
nearly constant light.
The bulb also flashes at the
point on the dial that indicates
the depth. The point is indicated
by the length of time it takes the
sound waves
to reach the bottom
and return. In addition, echoes
returned from any object
in the
water between the surface and
bottom fire the bulb, too. Since
these echoes are also timed, they
show the exact depth of
any fish
— or any number of fish — in
the water. And because the
sound waves from the transducer
go down into the water in a nar-
row cone angle, they tell, within
a matter of a few feet, the fish's
location as well as the depth.
At a depth of 10 feet, the cone
covers a circle that is approxi-
mately
one foot in diameter; at
15 feet it is two feet wide, at 20
feet, three feet wide, the cone
diameter is four feet wide. Re-
gardless of
depth, the cone of
sound ends at the bottom. But
an echo is also returned from
any object
between
the trans-
ducer and the bottom.

WEAK SIGNAL INDICATES GAIN TOO LOW Fig. 12 ak

$ t t
EAGLE "U:
I wArgRpIlOOF
EAGLE ELECThONOGG,,!G,!,.
Fish: 17 ft.
D,pth: 35
Fig. 15
11 8
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