Humminbird 343c Operation Manual page 7

When all the echoes are viewed side by
side, an easy to interpret "graph" of the
bottom, fish and structure appears.
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. Low frequencies
(83 kHz) are typically used to achieve
greater depth capability.
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