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May 21, 2010

Hi-Tech Transducers

How broadband and multifrequency transducers may change your fishing...

Material Matters
The ability to "tune" a transducer comes from the use of new materials in the transducer's ceramic elements that have dropped in cost over the past five years, Reedenauer says. Ceramic - an inorganic, nonmetallic solid - can convert electrical signals into mechanical vibrations and vice versa. Different ceramics operate optimally at different frequencies.

Airmar's current 2 and 3 kW, multiple-frequency, or "broadband," transducers consist of one high-frequency (130 to 210 kHz) ceramic element - think of a drink coaster - and a series of ceramic elements (an array) for the low-frequency side (options range from 28 to 75 kHz). Arrays typically handle more power than a single ceramic, so they sound deeper. On Airmar's R209 broadband transducer, for instance, the high-frequency single ceramic is rated at 2 kW of power, while the low-frequency, 24-element array is rated at 3 kW.

Reedenauer expects the company will soon introduce broadband transducers for the 600-watt to 1 kW market - the typical range of mainstream recreational machines. These transducers would pair with next-generation sounders from various sonar makers.

Eventually, recreational sounders may be able to broadcast and listen to multiple frequencies all at the same time. That capability currently exists with extremely expensive commercial units that also scan in multiple directions.

Consider the Q
One crucial characteristic of broadband transducers is their low Q factor: That translates into a crisper sonar picture. Here's the easy explanation: Think of a church bell. When you strike it, it rings and continues to resonate. If a transducer ceramic were like that bell and continued ringing, when its signal returned, it couldn't generate a clear picture. A low Q transducer (Q factor of 8 or less) stops vibrating very quickly, so the signal return translates clearly.

"A low-ringing broadband transducer - even a 600-watt transducer - would show bottomfish disconnected from rather than blurred into the bottom," Reedenauer says.

On average, broadband transducers do cost more. A 1 kW non-broadband transducer may cost roughly $700, while a broadband version, once introduced, may retail for about $1,000.

Other recent innovations - such as the tilted-element, low-profile transducer (Airmar's B164) - help place multi-element, higher-power transducers on smaller and smaller vessels. Previously, larger transducers required the use of a thick fairing block. A fairing block positions a through-hull transducer on a slanted hull so it shoots directly down to the bottom. But it gets in the way if you trailer or forklift your boat onto storage bunks or rollers and can hinder vessel performance on the water.

Airmar also created a series of multi-element, in-hull transducers built inside fluid-filled tanks (M260, R199, R299, R399) that mount anywhere inside the hull. Reedenauer says the configuration loses nothing on detail and only a very tiny amount of range.

Proper Pairing
Anglers shopping for a new sounder shouldn't automatically choose the lowest-cost transducer, the experts say. And anglers hoping to improve their current sounder's performance should explore new transducer options in addition to upgrading multifunction displays.

Electronics dealers and manu-facturers will walk their customers through the transducer choices, if asked, and will present good/better/best scenarios based on fishing practices, boat model and budget. Generally, though, the more surface area a transducer has that's exposed to water, the better the performance.

"On the receive side, anytime you can increase the surface area, you'll get a more sensitive transducer," says Wood. "Greater sensitivity without ringing equals better target detection whether you're looking at the bottom, fish or eel grass."

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Numbers Game
If the difference between high-frequency (200 kHz) and low-frequency (50 kHz) transducer signals constantly confuses you, take heart: You're not alone. Here's one way to keep these two common frequencies straight.

• If you fish deep water (more than 300 feet), think small number. A 50 kHz signal emits a wider beam that can penetrate the depths.

• If you fish shallow water (less than 300 feet), think big number. A 200 kHz signal emits a narrow beam that won't penetrate as deep but shows better detail.

Note: When using a dual-frequency transducer, split the display screen to show both frequencies for two different perspectives on the water column.