Transducer Tips & Info Part 3 Final Part

[NavShack]

Beamwidth and Frequency of a Transducer

A key element of any transducer is it’s beamwidth at a given frequency. Beamwidth is the size of the cone measured in degrees. Where a floodlight covers a wide area and therefore has a large beamwidth, a spotlight is more focused and has a narrow beamwidth. Not all of the signal is within the stated beamwidth of a transducer just as there is some dimmer light surrounding the main beam of a floodlight or spotlight. In case you were wondering. When the signal deminishes to half or less of the main beam, it’s no longer considered part of the beamwidth. That part of the cone outside the main beam is called the sidelobe. Targets that enter a sidelobe and reflect enough energy for the transducer to detect are still shown on the sounder display.

It’s important to know about beamwidth and even sidelobes to properly use and interpet targets shown on your sounder. For example: With a beamwidth of 40 degrees, the signal cone is 36 feet wide at 50 feet below the boat. That means a fish detected in the main beam may be directly below you or 18’ away from center. If that same fish is large enough and is detected within the outer limits of a sidelobe it could be 50’ to one side or another. Extend those numbers to 100 feet deep and the fish, or structure, you think you’re on top of may be 100 feet or more away. That’s when knowing how to operate and interpet your sounder really makes all the difference.

The reason behind using sounders and transducers that operate on both 50 kHz and 200 kHz is the inherent characteristics of the specific frequency. Lower frequencies (50 kHz) can detect targets at greater distances and higher frequencies (200 kHz) have greater resolution. Lower frequencies use wider beamwidths than do the higher frequencies. A basic transducer may have a 50 kHz beamwidth of 46 degrees and 12 degrees at 200 kHz. Higher quality transducers focus the beamwidth to say 20 degrees at 50 kHz and 8 degrees at 200 kHz. More power to the target means a better operating sounder. If you’re interested in running the numbers on your particular transducer, you can find a beamwidth calculator tool at the NavShack website.