Humminbird 141c - Manual (Page 58)

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Maximum Depth Menu: The Maximum Depth Menu is a Humminbird® feature that
optimizes performance based on the maximum operational depth set by the user. Many
Humminbird® units can operate across a very broad depth range (up to 2500 feet)
which causes the unit to "look" up to that full depth under some circumstances. Due to
the speed of sound in water, this can result in less responsiveness because the unit has
to wait for a longer period of time to receive the sonar signal. When the Maximum
Depth menu is set to a lower value, the unit only looks up to the setting, which increases
the responsiveness of the unit. This is an important feature for anyone operating in
shallower depths!
Noise: Noise is 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. Electrical noise (from trolling motors, bilge pumps, VHF radios)
typically manifests as a consistent dot pattern. Electrical noise can be isolated by
selectively turning on and off other electrical devices to determine the source. Often re-
routing the power cable, or connecting to an alternative power supply (second battery)
can help overcome electrical noise. Hydrodynamic noise (from propeller and/or hull
cavitation) has a more random appearance and is generally related to boat speed, so
that faster operation results in more noise. Hydrodynamic noise can be overcome by
proper transducer installation. Many Humminbird® products have a Noise Filter menu
setting that allows the user to clear the screen of noise that is difficult to eliminate.
Pixels: Pixels are 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. See Pixels, Vertical.
Pixels, Vertical: Vertical Pixels are a number of vertical picture elements in a single
column on an LCD display. More vertical pixels provide finer resolution of targets
detected by sonar. Essentially, a vertical distance (the depth), when divided by a larger
number, breaks that distance into smaller samples, each representing a smaller area
and thus providing more detail. In fishfinders, vertical pixels are more critical than
horizontal pixels because the horizontal axis of the display represents time, or history.
Sonar information on the horizontal axis can vary greatly, depending on boat speed and
the Chart Speed setting. A greater number of horizontal pixels show more sonar history
that the boat has passed through. On many models, Humminbird® provides the most
vertical pixels to provide a better display resolution. See Chart Speed and Pixels.