Humminbird 858c Combo, Installation And Operation Manual

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2 Introduction
The sound pulses are transmitted at various
frequencies depending on the application.
Very high frequencies (455 kHz) are used for
greatest definition, but the operating depth is
limited. High frequencies (200 kHz) are
commonly used on consumer sonar and
provide a good balance between depth
performance and resolution. Low frequencies
(83 kHz) are typically used to achieve greater
depth capability.
The power output is the amount of energy
generated by the sonar transmitter. It is
commonly measured using two methods:
• Root Mean Square (RMS) measures power
output over the entire transmit cycle.
• Peak to Peak measures power output at the
highest points.
The benefits of increased power output are
the ability to detect smaller targets at greater
distances, ability to overcome noise, better
high speed performance and enhanced depth
capability.
High Definition
Side Imaging
®
Sonar
(898c SI and 998c SI only)
The 898c SI Combo and 998c SI Combo
use Side Imaging® sonar to provide a
wide yet precise survey of a large area
of water, including detailed bottom
topography and fish-attracting structure
orientation.
The Side Imaging®
transducer returns are processed into an
image similar to an aerial photograph.
Typically, the Side Imaging® sonar can
search an area that is 480 feet wide (240
to each side), with a typical depth
performance of 150 feet when the Side
Imaging® Sonar frequency is set for
455kHz. The side beams can be
operated at one of two frequencies:
455 kHz or 800 kHz. Selecting 800 kHz
produces the sharpest image, but the
search area to each side and the depth
capability are limited as compared to the
455 kHz frequency. See
What’s on the
Side Imaging® Display and
Understanding Side Imaging® for more
information.
60°
83kHz
20°
200kHz
86°
455kHz
86°
455kHz