Garmin GPSMAP 178 Owner's Manual page 107

Transducers
The transducer acts as the eyes and ears of your new sonar. Proper transducer selection and installa-
tion are critical to the operation of your unit. The transducer transmits sound waves toward the bottom
in a cone shape. The larger the cone angle, the larger the coverage area at a given depth.
A wide cone angle transducer works best in shallow water. The wide cone angle provides a large
coverage area, but at a decreased bottom resolution. In deeper water this can result in a large dead zone
where fish cannot be seen. A narrow cone angle transducer is better suited to deep-water installations.
The narrow cone angle provides a smaller viewing area (compared to a wide cone angle transducer at the
same depth) with improved bottom resolution and a smaller dead zone. Dual frequency transducers give
you the best of both wide and narrow cone angles.
The GPSMAP 178/178C is packaged with and without a transducer. Depending on which transducer
you select, you will have either single or dual frequency performance. Since many mounting locations
vary, there are a variety of standard and optional transducers, and accessories which are available. See
your local Garmin dealer or contact Garmin to help you in your selection of optional transducers and
accessories.
Appendix A
Selecting a Transducer
Wide cone angle
Narrow cone angle
dead zone
X
fish not seen
X