How Fish Finders Work

By Andrei Loskoutov

The thrill of any fishing adventure begins with finding the right place to wet your line. Fish finders allow anglers to quickly identify key targets and structure, as well as fish. A fish finder is a subset of a group of instruments called SONAR.

SONAR consists of a transmitter, transducer, receiver and display. In the simplest terms, an electrical impulse from a transmitter is converted into a sound wave by the transducer and sent into the water. When this wave strikes an object, it rebounds. This echo strikes the transducer, which converts it back into an electric signal that is amplified by the receiver and sent to the display.

Since the speed of sound in water is constant (approximately 4800 feet per second), the time lapse between the transmitted signal and the received echo can be measured and the distance to the object determined. This process is repeated many times per second.


The display shows a history of the received echoes. The user can make a number of adjustments to tailor the display to his or her preference. These include sensitivity, depth range, and chart speed. Displays use a variety of technologies and provide different resolutions and number of shades of gray or colors. Each display is made up of a number of pixels, which are little square blocks that make the images. The more pixels and shades of gray or hues, the better the resolution and image clarity.

Fish Targets:

Echoes from fish within the beam will be shown on the display by illuminated pixels. What image appears on the display depends on a number of factors: the sensitivity setting on the fish finder, the cone angle of the transducer, the speed of the boat, and the size, depth, speed and direction of the fish. A fish that is swimming directly beneath the boat will create a consistent echo that will cause a continuous line to appear on the display.

A stationary fish caught in a narrow beam transducer appears as a single point on the screen as the boat passes above it. Under the same conditions the fish will appear as an arc if a wide beam transducer is used.

To read more about how fish finders work, or select a fish finder that right for you, you may visit our site at:

Almost anyone can now afford to own a unit that will assist in a better fishing.

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Copyright 2006, 2016 by Andrei Loskoutov. All rights reserved.