Higher frequency transducers have shorter wavelengths and more wave cycles per second, which means you can visualize more details (smaller fish) but have only shallow to moderate depth capacity. One sound wave at 200kHz is slightly longer than 1/4", so a 200kHz sound wave will be able to detect fish as short as a quarter of an inch. A 200kHz transducer has a range of only about 600'. High frequency provides a crisp, clear picture of the bottom with the tradeoff of less depth range. For best resolution, choose 800kHz or 455kHz transducers.
The Garmin Echo 551DV is one of the newer and more advanced models in the Garmin line of fish finders and it’s the top fish finder under 300. It’s one of my top choices and I really think that it’s the best fish finder for the money. It offers the best fishing sonar and a large clear display. The transducer has 500 watts of power, which allows the wave to go as deep as 2300 feet. It comes from the echo fish finder series that are known for their great accuracy.
Commercial and naval fathometers of yesteryear used a strip chart recorder where an advancing roll of paper was marked by a stylus to make a permanent copy of the depth, usually with some means of also recording time (Each mark or time 'tic' is proportional to distance traveled) so that the strip charts could be readily compared to navigation charts and maneuvering logs (speed changes). Much of the world's ocean depths have been mapped using such recording strips. Fathometers of this type usually offered multiple (chart advance) speed settings, and sometimes, multiple frequencies as well. (Deep Ocean—Low Frequency carries better, Shallows—high frequency shows smaller structures (like fish, submerged reefs, wrecks, or other bottom composition features of interest.) At high frequency settings, high chart speeds, such fathometers give a picture of the bottom and any intervening large or schooling fish that can be related to position. Fathometers of the constant recording type are still mandated for all large vessels (100+ tons displacement) in restricted waters (i.e. generally, within 15 miles (24 km) of land).
While catching a fish is often a case of matching wits—and great patience—a fisherman is at a distinct disadvantage without the right gear. eBay stocks the fishing supplies you need, like spinning rods, casting rods and more by St. Croix, Shimano and other top brands. There are plenty of saltwater and freshwater choices, so it doesn’t matter if you’re after salmon, trout or marlin.
Lower frequency transducers, with longer waves and fewer waves per second, show less detail (larger fish) but carry more energy and penetrate to greater depths. One sound wave at 50kHz is slightly larger than 1", so a 50kHz sound wave will only detect fish if their air bladders are large, slightly longer than an inch. Lower frequency won’t provide as clear of a picture but will operate effectively in the depths of the ocean or Lake Michigan.

Ultrasound frequency used by a fish finder generally ranges from 15 kHz to 200 kHz. However, the majority of the conventional fish finders oriented for recreational craft utilize 50 kHz and 200 kHz. Such fish finders available in the market incorporate electronic circuitry that can transmit and receive ultrasound in these two frequencies. Also, a transducer mounted on the bottom of the craft is configured to handle these two frequencies.
You probably already know how to use a Garmin chartplotter. It is that intuitive. Just turn it on and you can quickly follow the simple menu. Everything is at your fingertips to quickly and easily plan your route and set your course. And most Garmin echoMAP™ and GPSMAP® chartplotters are available combined with built-in sonar capabilities. These include advanced HD-ID™ sonar, CHIRP sonar and Garmin ClearVü™ and SideVü™ scanning sonar, which provides the clearest scanning sonar images on the water.
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Now let’s imagine another scenario – again your sonar is stationary, but this time 2 fish swim through your sonar beam, one big and one small. The big fish swims very quickly through the sonar beam, the small one swims slowly. Which one will make the longer fish arch on your screen? The answer is the small one. That’s because a slow moving object will leave a longer mark than a fast moving one, whatever their size.
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