What Is the Transducer on a Fish Finder?

The transducer is the business end of a fish finder. The transducer converts the electrical impulses from the fish finder into mechanical energy -- sound. The transducer is made up of a pinger, which generates a sound pulse of a specific frequency, and a receiver to catch the signal bounced back from that object. The transducer then converts the sound back into an electrical impulse that the fish finder turns into a visual display.

  1. Sonar

    • A fish finder is a scaled-down version of sonar, the underwater navigation system that depends on bouncing sound off underwater objects to determine their distance from the sonar system's "sound head." The sound head may be made up of a single transducer, or several transducers, each with a different orientation, to give the operator a picture of the object or feature being inspected. Sonar can be so concentrated that it can produce a camera-like picture of the object, revealing details as small as a half-inch in diameter.

    One Unit, Two Functions

    • The transducer on a fish finder can operate both as a "pinger," the transducer's active component that generates a coherent ultrasonic pulse and a receiver. Since the transducer on a fish finder is aimed straight down, this coherent ping goes straight down in a concentrated column of sound, called a "ping." The ping bounces straight up from the objects it encounters. When the ping returns from the bottom or objects between the bottom and the bottom of the boat, it's picked up by the transducer.

    The Receiver

    • The transducer's receiver is the same unit as the pinger. The construction uses the piezoelectric effect to both produce and receive the sound. The pinger function generates sound at a specific frequency. As it bounces back to the transducer, the ping's frequency is changed slightly by its encounter with the objects below the boat. Since a fish's tissue will absorb more of the ping than the mud of the bottom or the hard surface of a rock, the signal received by the transducer will be slightly different than the original ping.

    Types of Transducers

    • Transducers are often identified by the way they are mounted on a boat. One kind, called the through-hull transducer, is mounted on the bottom of the inside of the hull, so the sound waves pass through the hull. A second kind, called a transom-mount, is mounted on the boat's transom, the back wall of the boat, where the outboard motor is mounted. A third type is the bottom-mounted transducer that's mounted in a recess on the outside of the hull.