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Glossary
Sonar Terms:
Beam (Sonar Beam) The wide,cone-shaped projectionof sound waves formedas 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 the bottom. 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 other objects close to the bottom that fallwithin the dead zone will
probablynotbe visiblein thesonar beam.Precisionsonarbeams,such as theHumminbird®
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)FSTNis amonochromedisplaytechnology
characterized by black, high-contrast pixels. All monochrome fixed mount Humminbird®
products use FSTN technology.
Frequency Ameasureof thenumber ofsoundwavecycles persecond ofa sound impulse
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
capableof 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.
Glossary
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