Using Sonar; Understanding Sonar; Using Dual Frequency; Using Dual Beam - Garmin GPSMAP 3206 Owner's Manual

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This section covers the additional options for the GPSMAP 3206/3210 when
used with a GSD 20, GSD 21, or GSD 22 sounder module. Read the installation
instructions included with your sounder to install it.
NOTE: You must have a GSD 20, GSD 21, or GSD 22 sounder module
installed and connected to your GPSMAP 3206/3210 to use the sonar features.
The following section provides a general overview of sonar and the
things you need to know to help you use the sonar functionality of your
GPSMAP 3306/3210.

Understanding Sonar

The transducer mounted on your vessel sends sound waves down into the water
in a cone shape, similar to a flashlight beam (covering a smaller circular area at
the top and angling out to a larger circular area at the bottom). These sound waves
reflect off of any object that they hit, and then the waves travel back up to the
transducer. These objects could be fish, branches, the bottom, or any other object
that has a density that is different from the water. The transducer receives the
sound wave information, and then sends the information to the GSD 20, GSD 21,
or GSD 22 sounder module and then to the GPSMAP 3206/3210. The
GPSMAP 3206/3210 displays the information on the screen for you to see and
interpret. The type of transducer and the settings that you choose determine how
the information is displayed on the screen.

Using Dual Frequency

Dual frequency works best for deep water (for example, off-shore) applications.
The 200 kHz frequency allows you access to great detail about what is underneath
your boat. The 50 kHz frequency provides less detailed information, but
penetrates to greater depths with the same power. You can choose either or both
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frequencies to get the information that you want. If you choose dual frequency,
the transducer alternates between the 50 kHz and 200 kHz signals. This capability
allows you to see the best picture available at any depth.

Using Dual Beam

Dual beam works best for shallow water (for example, inland) applications.
A dual beam transducer can transmit a narrow or a wide beam. The water area
covered by the transmitted sound waves is determined by the beam width of the
transducer and the water depth. The narrow beam provides crisp detail of what is
under your boat, and is very helpful if you are fishing in deeper water where the
beam covers more area (for example, at a 30-foot depth, the narrow beam covers
the area of about a 7-foot circle).
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GPSMAP 3206/3210 Owner's Manual