The diagram shows the coverage area of 2D sonar, down-imaging sonar
and side-imaging sonar. (Courtesy Humminbird Electronics)
Understanding Sonar Beams and Cones
by Brad Wiegmann
Anglers often think that the signals being emitted from your electronics’ transducer are all the same. But that’s not at all true.
The shapes of sonar beams and cones vary, changing according to what mode and frequency the fishfinder is in. Selecting the right mode and frequency allow anglers to see below, side-to-side and in front of the boat.
Traditional 2D sonar and CHIRP sonar with single element transducer has a conical shape. In fresh water anglers normally use 83kHZ/Medium CHIRP or 200kHz/High CHIRP when fishing. The small size 83kHz/Medium CHIRP cone is narrower, but shows greater detail than the larger 83kHz/Medium CHIRP.
When a boat is moving, fish echoes (images on your screen) inside the cone will be arches or partial arches – created as your transducer approaches the fish and then moves away after passing over the fish. However, if your boat is stationary, the echoes will be a straight line.
Down-scan and side-scan imaging use narrow, elongated beams to produce photograph like imaging sonar. To produce these images, a long, oval shaped transducer is required.
Side-scanning sonar is available in 455kHz, 800kHz or 1.2MHz from Garmin, Lowrance, Humminbird and Raymarine. The higher 1.2MHz produces superb clarity and target separation.
Side-scanning uses a linear down and circular image that results in a narrow, elongated fan-shaped pattern beam. The narrow, elongated fan begins at the boats keel outward until it runs out of range or bounces off a solid object like a bluff wall.
Fishfinders view of side imaging can be difficult for novice angler with sonar to understand. Side imaging takes the left scan and right scan of the boat than stitches it together with down scanning imaging. When stitched together the left and right scan will be lighter the dark center which represents the column below the boat.
Live-imaging sonar (LIS) requires a special transducer to produce an image allowing anglers to scan for fish, find fish and see how they react to lures. LIS transducers produce an elliptically-shaped, 3-array beams with individual transducer elements within one larger transducer. When the beams are stitched together the end result appears as one image, however, this stitching results in interference blind spots.
Beam angle directions are controlled by the angler with LIS. Anglers can adjust angles to be forward, down or in Panoptix/Scout/Landscape. Garmin, Lowrance and Humminbird include a bracket to attach the LIS transducer to a trolling motor on the port or starboard side of the shaft.
Reading and studying the signals emitted from your transducer(s) in different brands or different modes will help you better understand and interpret what you see when you’re fishing.
From Springdale, Arkansas, Brad Wiegmann is a professional photographer, videographer and outdoor writer published in dozens of print and electronic media outlets all across the nation. He is also a well-known guide, podcaster and social media influencer. Learn more about Wiegmann and his lengthy experience and expertise at BradWiegmann.com.
