Humminbird 161 Operation Manual page 102

than freshwater due to continuous wind and wave action that causes aeration at the
surface. The Surface Clutter menu provides manual control to bias the default
settings under extreme conditions.
Target Separation: Target Separation is the measurement of minimum distance
that a fishfinder needs to be able to recognize two very close objects as two distinct
targets (i.e. two fish hanging very close, or a fish hanging very close to structure).
Humminbird® fishfinders provide a very good 2 1/2 inches of target separation in
shallower than 100 feet of depth. Target separation decreases as depth increases
due to the need for longer Pulse Width to achieve greater depth. See Pulse Width.
Thermoclines: Thermoclines are water layer(s) of distinctly different temperatures
that create a sonar reflection due to the density of the differing water temperatures.
Typically a thermocline will appear as a continuous band across the display at some
distance above the bottom contour. Thermoclines are of interest to anglers because
fish will suspend above or below the thermocline as they seek the optimum
temperature and oxygen levels.
Time Variable Gain: Time Variable Gain is a processing step applied to the sonar
return to "normalize" the data so that objects of equal size (i.e. fish) appear to be the
same size, even if they are separated by a good distance. Time Variable Gain is a
fundamental attribute of good sonar, but is often promoted as a feature.
Total Screen Update®: A Humminbird® feature that refreshes and updates all the sonar
information on the display when a range change occurs. Without Total Screen Update®,
only the most recent sonar information would be drawn to the new range, and the old
sonar information would continue to scroll off the screen at the old range.
Transducer: The transducer is part of the sonar system, which mounts on the boat
and is in contact with the water, that converts the electrical energy from the
transmitter into sound energy, and that forms the sonar beam in turn. Internally,
the transducer consists of one or more piezo electric disks that expand by very
minute amounts to create the sound wave. This element also works in reverse,
converting the returned sound energy back into an electrical signal that the receiver
interprets. Transducers are available for many specific mounting applications for the
boat, such as a transom mount, trolling motor mount, etc. Humminbird® offers
many sophisticated transducers, often with multiple piezo electric elements
designed to form specifically-shaped sonar beams, providing the angler with
superior tools for finding and catching fish. See Transmitter and SONAR.
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