JW Fishers SCAN-650, Руководство по эксплуатации

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12
Fish
100 m
10 m
Target #1
Target #2
Acoustic Wave 100 m Range Switch
Transducer
25 meter range
3 meters
The JW Fishers SCAN-650 scanning sonar operates by transmitting a short, high energy,
narrow width acoustic wave. This high energy acoustic wave hits directly below the transducer
first (as shown below)
As the pulse continues to sweep across the bottom, away from the transducer, echoes
continuously return to the transducer (see below). The returning echos strike the transducer
which produce the return electrical signals.
The harder the object (rocks, metal, etc ), the larger the returned echo. The angle of the
bottom surface and target angles also impact the amplitude of the return signal. The left
side of target #1 and #2 will produce a larger (harder) return echo than the top area. When
the acoustic wave hits the top of the target, some of the echo is reflected away from the
fish. When the bottom slopes away and down from the fish, only light echo’s return from the
bottom. When the bottom slopes upward, medium echo returns are received. If a hard
target is positioned on a down or on a up-sloping bottom, a hard return will result from the
target. If a target is up “off the bottom”, as is target #1 and #2, then there will be an area
directly behind the target that will be blocked from the acoustic wave. No echo returns will
be received from that area by the fish. When displaying this area, the display will show a no
signal color. This area on the display is called the target’s “shadow”.
The return electrical signals are amplified by the preamp and sent up the cable to be
processed by the “time variable gain” (TVG) circuit in the Sonar Processor. (Refer to
page 15 for a more details on the TVG circuit.)
THEORY OF OPERATION (continued)
10m
#1
#2
100 m Range Switch
Returning Echos
Fish
Acoustic
Wave
100 m
Hard Return
No Return Echos (Shadow)
Light Return
Medium Return
Hard Return
A look at returning echoes
Transducer
25 meter range
3 meters