Glossary - Humminbird HELIX 5 SI GPS Operation Manual

Glossary

Beam (Sonar Beam)
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
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 fall within the dead zone will 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
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)
black, high-contrast pixels. All monochrome fixed mount Humminbird products use FSTN technology.
Frequency
A measure of the number of sound wave cycles per second of a 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 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.
Grayscale
The use of varying shades of gray to represent the strength of the sonar signal on the display.
Traditionally, the strongest sonar signals are represented in black, and progressively weaker signals are
represented in progressively lighter shades of gray.
Noise
The unintentional, external sound waves that interfere with the optimal operation of sonar. Noise
appears as random "dots" on the display and is caused by a variety of sources. Many Humminbird products
have a Noise Filter menu setting that allows the user to clear the screen of noise that is difficult to eliminate
(also, see Troubleshooting).
Pixels
The "picture elements", or small square blocks, that make up the image on the LCD. Measured as a
vertical by horizontal number (i.e. 640V x 320H), this key specification typically indicates the quality of
resolution. In fishfinders, the total resolution (vertical multiplied by horizontal) is often less important than the
"Vertical Pixel" resolution because a greater number of vertical pixels provide finer resolution of targets
detected by sonar. Sonar information on the horizontal axis can vary greatly, depending on boat speed and
the Chart Speed setting.
Glossary - Sonar
The wide, cone-shaped projection of sound waves formed as sound travels
FSTN is a monochrome display technology characterized by
162
Sonar
dB
dB Down Point
.