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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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