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Glossary
Sonar Terms:
Beam (Sonar Beam) The wide,cone-shapedprojectionof sound wavesformed as sound
travels underwater. See
Cone Angle.
Bottom Contour The profile of the bottom graphed to the display as the depth changes.
Bottom Hardness The density (or composition) of thebottom.Varying levels of 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. -10 dB). See
dB Down Point.
Dead Zone The area of the sonar beam that receives the sonar signal after the main
bottom return. Fish and otherobjectsclose to the bottomthat fallwithin the deadzone will
probablynotbe visible in thesonarbeam. Precisionsonarbeams,suchasthe 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 “@ -10 dB” or “@ -3 dB“. Measurements at smaller down points (bigger
negative numbers) indicate that the less intensive sonar signals are being used for the
measurement.
Display, FSTN (Film Super-Twist Nematic)FSTN isa monochromedisplaytechnology
characterized by black, high-contrast pixels. All monochrome fixed mount Humminbird®
products use FSTN technology.
Frequency A measureofthenumberof soundwavecycles persecondofa sound impulse
transmitted underwater. Atypical frequency for fishfinders is200 kHz, which offers a good
balance of performance under many conditions. Lower frequencies, such as 50 kHz, are
capable of penetrating to greaterdepths,but with less resolution. Higherfrequencies, 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.
Glossary - Sonar