Humminbird 500 SERIES 580 - Manual (Page 9)

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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 performance and resolution.
Low frequencies (83 kHz) are typically used to
achieve greater depth capability.