Fish finders are basically a type of SONAR (sound navigation and ranging). Fishfinders use "active" (rather than passive which does not produce thesound) sonar to detect fish. Fish finders also detect the bottom of the oceanor lake, and everything else that reflects the sound beam.
The transducer (usually included with the fish finder)produces the sound beam which reflects off anything under the boat. Thesereflections are interpreted and displayed on the graphic display (usually a LCDor CRT screen) of the fish finder.
Fish finders get their origins from fathometers. Modern fathometers (meaningfathom plus meter) are designed specifically to show depth and usually onlyhave a digital display. Early fathometers were comprised of a flashing rotatinglight at the edge of a circle.
This was synced up with the received echo andcorresponded to the depth of the water. They also gave a faint flicker of lightfor echo's off fish. After technology advanced enough CRTs were used with afathometer and thus the fish finder was born. In the early 1990's CRTs werereplaced by lower power LCD displays which also brought the price down to amore affordable range.
