Principle of Operation

The FCV-582L determines the distance be- tween its transducer and underwater objects such as fish, lake bottom or seabed and dis- plays the results on its screen. It does this by utilizing the fact that an ultrasonic wave trans- mitted through water travels at a nearly con- stant speed of 4800 feet (1500 meters) per second. When a sound wave strikes an un- derwater object such as fish or sea bottom, part of the sound wave is reflected back to- ward the source. 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 electri- cal signal produced by the transmitter is con- verted 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 sig- nal. The signals are then amplified in the am- plifier section, and finally, displayed on the screen.

The picture displayed is made up of a series of vertical scan lines, one for each transmis- sion. Each line represents a snapshot of what has occurred beneath the boat. Series of snap- shots are accumulated side by side across the screen, and the resulting contours of the bot- tom and fish between the bottom and surface are displayed.

Underwater conditions and video sounder display