Furuno GP-1650WDF - Manual (Page 15)

2-1
2. VIDEO SOUNDER OPERATION
2.1 Principle of Operation
The video sounder determines the distance
between its transducer and underwater
objects such as fish, lake bottom or seabed
and displays the results on screen. It does
this by utilizing the fact that an ultrasonic
wave transmitted through water travels at a
nearly constant speed of 4800 feet (1500
meters) per second. When a sound wave
strikes an underwater object such as fish or
sea bottom, part of the sound wave is
reflected back toward the source
(transducer). Thus by calculating the time
difference between the transmission of a
sound wave and the reception of the
reflected sound wave, the depth to the object
can be determined.
The entire process begins in the display unit.
Transmitter power is sent to the transducer
as a short pulse of electrical energy. The
electrical signal produced by the transmitter
is converted into an ultrasonic signal by the
transducer and transmitted into the water.
Any returning signals from intervening
objects (such as a fish school) are received
by the transducer and converted into an
electrical signal. The signals are then
amplified in the amplifier section, and finally,
displayed on screen.
The picture displayed is made up of a series
of vertical scan lines, one for each
transmission. Each line represents a
snapshot of what has occurred beneath the
boat. A series of snapshots are accumulated
side by side across the screen, and the
resulting contours of the bottom and fish
between the bottom and surface are
displayed.
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Underwater conditions and video sounder display