Transducers in a Nutshell

The information about fish finder transducers can be both overwhelming and difficult to understand.  This article lays out the different aspects of transducers and offers some suggestions on the type of model you may need.  These guidelines can be used for both fixed mount and portable fish finders.

LOW frequency vs. HIGH frequency

Transducers come in Low and High frequencies.  Low frequencies generally range from 50 to 100 kHz.  High frequency models generally range from 180 to 200 kHz. Lower frequency sound waves can travel greater distances.  They penetrate further in the water.


You need to also keep in mind that fish finders are generally designed to work with specific frequencies (or a couple of frequencies).  

IMPORTANT: If you purchase a transducer separately, or you already have one, make sure your model will work with the frequency guidelines of your fish finder.  This applies for portable fish finders as well as mounted models.

Cone Angle

A transducer works by concentrating a sound wave into a beam and emitting this beam into the water.  This beam is emitted in a small arc (measured in degrees) from the transducer. As the beam travels deeper into the water, the arc covers a wider area.  If you plot the area the beam covers on graph paper it will look like a cone, thus the term “cone angle”.  If you draw a line from the very tip of the cone down to the cone bottom you have identified the center line of the cone.  The emitted sound wave is strongest closeo this center line and diminishes as the distance from center line increases.

Cone Angle becomes important because the greater the angle the bigger the coverage area and therefore the bigger the area that the fish finder can “see”.  As you move further away from the center line, the clarity of the image decreases.  

Large Cone 40o - 60o	Larger Coverage Area Less Clarity at Greater Depths
Narrow Cone 15o - 30o	Smaller Coverage Area More Clarity at Greater Depths

Frequency and Cone Angle Working Together

High Frequency transducers come with either a narrow or wide cone angle.  
For shallow water fishing, a high frequency (180 - 200 kHz), narrow cone angle (20^o - 30^o) model may be a good choice.  You will not be able to see great depths, but you’re in shallow water.  The narrow cone angle will allow you to see things more crisply than a wide cone and will allow you to be able to distinguish the objects you see on the display easier.  If you really want to see a large area, then think about a wide cone angle instead.

For deep water fishing you will most likely want to search the highest volume of water possible in the shortest amount of time. Consider fish finders that have a low frequency (50 - 100 kHz) for greater depths, and a wide cone angle (40^o - 60^o) for greater horizontal distances from the cone center line.  This combination will allow you to see at greater depths, but the definition (how crisp the image is on the fish finder’s display) will not be as good.  You can increase the definition by buying a fish finder with a higher sensitivity display.

Here’s a quick summary:

High Frequency / Narrow Cone Angle	Low Frequency / Wide Cone Angle
Shallower Depths Better definition (crispness) and object separation on the display Less susceptible to outside interference	Deeper depths Less definition (crispness) and object separation on the display More susceptible to outside interference

	Fresh Water		Salt Water
	Shallow Water	Deep Water	Shallow Water	Deep Water
Frequency	High	High or Low	High or Low	Low
Cone Angle	Wide or Narrow	Narrow	Wide or Narrow	Wide

 

Dual Frequency Transducers

Low frequency, wide cone angle setups do have some limitations.  For example, you can cover a wide area and a greater depth which gets you into the “general” area of where the fish are, but we don’t want to fish in the general area, we want to put our lines directly in front of the fish.

To do that, fish finder manufacturers developed Dual Frequency Transducers.  (Humminbird Fish Finders refer to these models as dual beam rather than dual frequency.) Dual frequency models, as the name implies, have two different beams that project at different frequencies.  One is set to a low frequency and the other to a high frequency.  Many fish finders will allow the fisherman to switch between the two beams on the display.  There are also models that have a split screen display that allow the angler to see images from both beams separately at the same time.  Some manufacturers even have displays that combine the imagines from the two beams into one image.  The display essentially combines the high-frequency detail with the wider beam and deeper search capabilities of low frequency.

For deep water fishing, dual frequency transducers are a great option.  They let you find the general area of the fish over a large volume of water using a low frequency-wide beam setting, and then, for greater accuracy, pinpoint the depth and location using a high beam-narrow cone setting for greater clarity.  

For shallow water fishing, a dual frequency transducer may be overkill.  There is little need to see fish at a depth greater than a hundred feet so a single beam, high frequency model may a better option.

 

 

Output Wattage

The depth your fishfinder will reach will be affected by water temperature, salinity, frequency, and power output which is measured in Watts. The following general guidelines will give you the maximum depth that can be reached:

Most recreational fishfinders come with a transducer with a wattage rating that matches the output wattage of the fish finder.  However, when purchasing a transducer separately, make sure the power output of the fish finder unit is less than or equal to the wattage of the transducer, otherwise the transducer may be damaged.

Overall, there are a lot of choices in fish finders.  The transducer is one of the key components of fish finders, whether they are fixed mount of portable fish finders.  Make sure you know what type of fishing you are planning and then select a fish finder based on your specific fishing needs.