Transducers Key to Quality Electronics

Workshop reveals new understanding of “cone angles”

by Tom Zenanko


At a recent outdoor press event at Devils Lake North Dakota, writers were treated to a new and different way of looking at the world of marine electronics. As the public relations point-man for Vexilar Marine, it is always a challenge to come up with new and exciting ways for outdoor writers to take a new look at something as boring and technical as marine electronics. The answer to this challenge was the first-ever transducer workshop.

Before we get into the actual results of our on-the-water testing, it is good to gain some background knowledge about transducers and how they work. I was amazed by the fact that so little information is commonly available. For this reason, anglers have developed their own reasons for why transducers do what they do. You will soon learn that nearly all of them are completely false! Much of the information for this story has been pulled from manufacturer’s technical data and interviews from experts in the field of sonar. It might seem a little deep at times, but knowledge is power and it will increase your understanding of how and why sonar works.

Understanding Transducers

The transducer is one of the most mysterious but important elements of marine sonar. The transducer is responsible for taking pulses of electrical energy and converting them to sound, then receiving the sound as it bounces back and turning those signals of sound back into electrical energy. After sending out a single burst or pulse of sound energy, the transducer is switched over to act as a microphone to pick up the returning sound as it bounces back from the bottom (or other objects that are between surface and bottom). The returning sound signals are very weak, so they are amplified and converted back into electrical energy. The internal software of your sonar then takes the incoming information and displays it as marks on a Liquid Crystal Display––or in the case of a flasher, LED lights.

Transducers come in many different frequencies as well as signal beam shape. Frequencies are often matched to the type of waters you fish. The lower the frequencies, like with a 50 kHz transducer, the less power loss you will have in deep water. Wide-angle cone angles often have lower frequency transducers, because a wide-angle cone signal will also lose power quickly. Low frequencies are best suited to observe or view a larger area below your boat with less power (or signal) loss. The high frequency transducer (like a 400 kHz), is better suited to inland fishing or shallow water applications, because the power loss can be noticeable in water deeper than 40 feet. High frequencies are best for giving you great bottom detail and are common with narrow cone angled transducers.

Anglers will find that most transducers are about 200 kHz in frequency, making them good for most fishing applications. The actual shape of any outgoing transducer signal is a lot different than many think. The sound being sent shoots out in all directions and there is no defined ‘cone’ or direction of the signal. The signal leaves the transducer at full power and in a very wide pattern. What you do have control over is how much of the incoming signal you want to hear. This is where the ‘cone’ angle size comes into play.

Each transducer can be designed to receive signals from a wide to narrow coverage area. Anglers do have some flexibility in matching the reception ‘cone’ the transducer is designed to receive. Again, the ‘cone’ is a common term that many people think describes outgoing signal, but it is actually the shape of how the transducer receives the sound signal as it bounces back to the transducer. The frequency and the shape of the cone angle work hand in hand to give anglers the right kind of results for their type of fishing.

Here are a few examples: If you’re fishing a lake with suspended fish, it is best to have a low frequency unit with a wide ‘cone’ angle. Then you have the right frequency and cone shape to spot targets that suspend high in the water column. If you’re an ice fisherman looking to spot a tiny ice fly very close to the bottom, a higher frequency transducer will give you better resolution, especially when it is matched with a narrow cone angle.

‘Gain’ settings are a big misconception with many anglers. The rumor is that the lower the gain, the less power the unit is outputting. This is totally incorrect. As you turn up the gain, what actually happens? You increase the unit’s ability to ‘hear’ more of the transmitted signal. As we already mentioned, the transducer emits a consistent outgoing signal at full power all the time. In other words, the amount of ‘noise’ bouncing around in the water remains consistent––and adjusting the gain is similar to turning a hearing aid up or down.

During our transducer testing, we turned the gain up as high as possible to ‘hear’ as much as we could from the signals being sent by the transducer.

Because the signal output being emitted by a given transducer crystal is always the same, it is good to know that the shape of the housing will not effect what the transducer crystal is trying to do, but it will effect how well it does its job. The housing the transducer crystal is mounted in should change to match the type of installation or use you have for your sonar. Vexilar is a leader in transducer design, and innovative ways of making products easier for anglers to use. Vexilar has three basic transducer shapes to handle nearly all fishing situations. First you have a high-speed transducer shape for mounting on the outside of boats. This sleek design permits water to flow smoothly over the surface of the transducer to give the angler a good reading at speeds up to 50 miles per hour. Then, you have the puck-shaped transducer that is mounted to an electric trolling motor or for mounting permanently into the hull of the boat. With a thru-hull mount (common on fiberglass boats), a transducer––when mounted properly––can work at speeds over 80 mph. Both of these transducer shapes would work during the winter months, but for best results you need to keep the transducer signals pointing straight down the hole. To give you superior ice-fishing transducer performance, Vexilar developed the ‘Ice-Ducer’. This revolutionary design is a balanced and weighted transducer that allows you to simply and easily hang the transducer down a hole in the ice. Gravity will automatically put the transducer in a perfect position for sending signals straight down the hole.

The Big Test

For this transducer workshop, we used the popular Vexilar FL-8slt three-color LED flasher, which uses a 200 kHz transducer frequency. 200 kHz is used by many of the most popular sonar brands and is a good all-around choice for most inland fishing situations. With this transducer, we used Vexilar’s popular Ice-Ducer with a 19-degree cone angle.

Preliminary research from manuals and talking with vendors revealed just how variable the transducer element can be from one transducer to another. This can be due to slight changes in design, construction and current condition of the transducer. Anglers might find it interesting to discover the true shape and size of their own personal ‘cone angle.’

Before venturing out into the brutal –40 degree wind-chills of North Dakota for this unique test, we needed to prepare. A target line was made using a marked line with one-foot intervals. A heavy 1-inch diameter metal disk was added to the line and would prove to be a strong target to reflect signals. The test started by finding a deeper water region of Devils Lake over 20 feet. With the help of the legendary “Perch Patrol,” a long continuous hole was cut using a StrikeMaster Lazer power auger that spanned 12 feet.*

Then, a tape measure was run along the length of the 12-foot hole.

With the hole cut and the tape measure in place, we proceeded to lower the target in one-foot increments and recorded the distance the target was from the transducer. Due to the extreme cold; we only recorded the target depth and the distance we were from the transducer.

The entire test took about ten minutes. If you duplicate this test for yourself, don’t be confused or misled by the depths you see the target at on the dial. They will be different, because the target is much farther from the center of the transducer signal, which is your shallowest point. The unit will display the distance the target is from the transducer and not from the surface.

Focus on your ability to see any part of the target. Set your transducer gain levels up as high as needed. There will be many other stray signals around the dial as you increase the gain, but if you slowly move your target up and down, you will be able to spot the target even in heavy clutter.

-The gain setting on the FL-8 acts like an amplifier of the incoming signals given off by the transducer. The higher the gain, the more you amplify the weaker signals to ‘hear’ signals at the edge of the signal reception range. This is an important point to remember, because Vexilar’s exclusive three-color flasher system actually lets you see weaker signals that are often filtered out by other brands of marine electronics. The fact that the weakest signals show up as green is something that also will change as you increase (turn up) the gain setting. The stronger the signal, the more orange and red you will see. Red tells you the targets are very strong––and often directly below the transducer. This ability to detect when a target is under your transducer is greatly diminished with a mono colored display. For this test, we were watching for green targets at the very edge of the transducer signal––we wanted to know when we could ‘just barely’ detect the metal disk.

While recording the results, you’ll be able to sense something is happening, but you really need to put the results onto a chart to visualize the true shape of the signal ‘cone.’

What did the test tell us? Well, for starters, the area you receive signals from is much larger than most anglers probably think it is. This is especially true in shallow water. So many times we visualize the ‘cone’ being just that––a cone shape. The real shape of the signal ‘zone’ is one of multiple lobes. It actually has a very irregular shape.

Because it’s so irregular in shape, for example, you might be able to spot a walleye that’s 9 feet away in 15 feet of water––but not see the same fish when it’s just 5 feet away in 19 feet of water!

Transducer crystals can vary a great deal from one brand to another and from one transducer to another. This is why we did the test, and we hope it will encourage others to give their own units the same type of test. At Vexilar, it is our hope that more anglers will take the time to better understand how their own sonar works. We know that, in time, this experience will give you the extra advantage you need to be more successful.

Notes: Vexilar is a leader in marine electronics and has a complete selection of both flasher type sonar (like the FL-8 and new FL-18 three color flashers) and its top-of-the-line liquid crystal unit, the Edge, or LC-507. The Edge is actually two separate sonar units in one, an innovative concept that’s catching on fast. This technology enables you to watch a wide-angle, low frequency transducer and narrow-beam, high frequency transducer signal at the same time. With two separate transducers running side-by-side, you can see big differences in bottom and suspended target identification. One side of the split-screen display will show you small changes in bottom content and give fantastic target separation. On the other side of the display, you are able to watch for suspended fish without making a single adjustment. Two very different transducers can give fishermen far more information than any single transducer by itself.

* Please, if you do this type of testing on your own, clearly mark the long, continuous hole before you leave the area, for safety’s sake.

Winter Fishing Systems, Inc 2016