Glossary
Sonar Terms:
Beam (Sonar Beam) The wide,
Bottom Contour The profile of the bottom graphed to the display as the depth changes.
Bottom Hardness The density (or composition) of the bottom. Varying levelsof hardness can be determined by interpreting the “thickness“ of the main sonar return. Hard returns appear thin and black, softer returns appear thicker and less black. It is important to note that a sonar return from a sloping bottom can have the appearance of a softer bottom.
Cavitation The effect of air bubbles created as the propeller rotates and the boat moves through the water.
Cone Angle The angular measurement of the sonar beam at a specific dB down point (i.e.
Dead Zone The area of the sonar beam that receives the sonar signal after the main bottom return. Fish and other objects close to the bottom that fall within the dead zonewill probably not be visible in the sonar beam. Precision sonar beams, such as the Humminbird® 20° beam, have a smaller dead zone than wider sonar beams.
Decibel The measurement for sound pressure level, or “intensity”of the sonar return.See
dB Down Point.
dB Down Point The standard decibel level at which the sonar cone angle is measured, and is written as “@
Display, FSTN (Film
Frequency A measure of the number of sound wave cycles per second of a soundimpulse transmitted underwater. A typical frequency for fishfinders is 200 kHz, which offers a good balance of performance under many conditions. Lower frequencies, such as 50 kHz, are capable of penetrating to greater depths, but with less resolution. Higher frequencies, such as 455 kHz, offer greater resolution, but are limited in depth performance. Humminbird® uses a variety of frequencies that are optimized for specific applications.
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