GPSMAP 292/298 Owner’s Manual 81
USING SONAR > UNDERSTANDING SONAR
Using Dual Frequency
Dual frequency works best for deep water (or off-shore)
applications. The 200 kHz frequency provides great bottom detail.
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 (or inland) applications.
A dual beam transducer can transmit either 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 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.
