Lowrance electronic LCX-17M - Manual (Page 80)

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Sonar Features menu with Fish I.D. Depths selected (left). When the
check box to the left is unchecked, the feature is off. Sonar Page
showing Fish I.D. symbols and FishTrack depths turned on (right).
Frequency (Change Transducer Frequency)
(Dual-Frequency Transducers only)
A dual-frequency transducer operates with both 200 kHz and 50 kHz.
The 200 kHz frequency has a 12
° cone angle and the 50 kHz frequency
has a 35
° cone angle.
The default frequency is 200 kHz, which is best for use in shallow water
(about 300 feet or less). This frequency is the best choice for about 80
percent of the fresh and salt water sport fishing applications. When you
get into very deep salt water, 300 to 500 feet or deeper, the 50 kHz
frequency is the best choice.
The 200 kHz transducer will give you better detail and definition, but
less depth penetration. The 50 kHz transducer will give you greater
depth penetration, but a little less detail and less definition. (Remember,
all sonar units typically read deeper in fresh water than in salt water.)
There is a common exception to these rules of thumb. Some fishermen
on freshwater lakes (or the ocean) using downriggers like to see them
on the sonar. In many of those cases, you'll see a 50 kHz transducer
frequency in use because the wider cone angle lets them watch the bait.
Symbols with
FishTrack depths