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Using sonar, Understanding sonar, Using dual frequency – Garmin GPSMAP 2210 User Manual

Page 80: Using dual beam, For more information

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GPSMAP 2206/2210 Owner’s Manual

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This section covers the additional options for the GPSMAP 2206/2210 when

used with a GSD 20, GSD 21 or GSD 22 Sounder Module. Read the installation

instructions included with your Garmin Sounder Module to install it

NOTE: You must have a GSD 20, GSD 21, or GSD 22 Sounder Module

installed and connected to your GPSMAP 2206/2210 to use the sonar features.

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 2206/2210. The

GPSMAP 2206/2210 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 appears on the screen.

Using Dual Frequency

Dual frequency works best for deep water (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

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).

Wide

Beam

Narrow

Beam

The wide beam is more helpful in shallow water, because it gives you a much

wider view of objects in the water, including areas beyond the sides of your boat.

At a 30-foot depth, the wide beam covers the area of approximately a 20-foot

circle.