Fishing Electronics part 2

Fishing Electronics part 2

Without getting technical, here is my understanding of how depth finders work. A depth finder powers a transducer that is located either on the back of the boat, the trolling motor, or it shoots through the hull. The transducer transmits sonar (SOund, NAvigation, and Ranging) waves in the shape of a cone. The waves get spaced out more as they go deeper. When the waves strike an object (fish, structure, bottom, etc.), they are reflected back to a receiver in the transducer. The signal is then sent to the unit and displayed for us to see. These waves are sent at high speeds so that they are displayed several times per second. Most depth finders will display each echo as a pixel on the right side of the screen and the chart will move to the left. The right side will show what is currently in the cone. What you see on the left has already passed through the cone.
Most units come in either high frequency (192-200kHz), low frequency (50kHz), or dual frequency (50/200kHz). This can be very confusing because cone angles can be considerably different at the same frequency. Narrow cones are better suited for deep water applications while wider cones are better for shallow water. If you are fishing for bass, you will probably want a high frequency unit with about a 60 degree cone. If you fish deep salt water, you may consider the low frequency or dual frequency unit.
With a 60 degree cone angle, you will see approximately 1.15 times the depth. For example, at 10 ft deep the cone will spread out to reach 11.5 feet across. At 20 ft deep, it would span a diameter of 23 ft across. A narrower cone angle of 30 degrees would show approximately 1/2 times the depth. At 20 ft, it would span a diameter of 10 ft. Conversely, a wider a cone angle of 90 degrees would show 2 times the depth. That would span a diameter of 40 ft at 20 ft deep. If you turn down the sensitivity, it will narrow the cone angle.