Humminbird HELIX 9 Operation Manual page 30

Down Imaging Sonar (HELIX DI GPS)
The Down Imaging transducer scans the water with razor-thin, high-definition
beams. The beams are wide (side to side) but very thin front to back.
The Down Imaging beams (shown in green) can be operated at two frequencies:
455 kHz (75°) or 800 kHz (45°). Select 455 kHz for the best overall image quality
and depth. Select 800 kHz for the sharpest image. See Set up Sonar for more
45°
800kHz
information.
75°
455kHz
The transducer also uses conical beams to provide data in traditional 2D format
16°
(shown in magenta and yellow). Select 455 kHz for a narrowly focused 16° center
455kHz
28°
beam, or select 200 kHz for a wider 28° beam (see Set up Sonar and Sonar
200kHz
Overview).
75 Degree Total Coverage
Sonar Overview 30