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All fishfinders operate using Sonar. Developed during World War II, this technology
uses sound waves to "view" underwater objects. A sound wave is produced by the
fishfinder and sent through the water. At the source, the wave is narrow; however as
it penetrates deeper, the sound wave spreads forming a cone, or what is commonly
called a beam (think flashlight). When the sound wave encounters something within
this beam, it bounces back to the fishfinder. By measuring the very small amount of
time between when the sound wave was send out and when it bounces back your
fishfinder calculates the distance and draws it on the screen.

If the signal doesn't encounter anything along the way, it reaches the bottom. Soft
bottoms like mud and weeds tend to absorb the signal. Hard bottoms such as rock
reflect a stronger signal back. These subtle differences in sonar reflections appear on
the display screen. That's how a fishfinder "reads" the bottom and everything in
between.

Cone Angles

The cone angle is the angular measurement of the sonar beam in degrees. For
instance, a 24 degree beam is broader and covers more area than 16 degree beam.
Cone angles are measured at "-10db", which is a method to assure consistency of
measurement from one transducer to another, and accurately represent the capability
of the fishfinder.

That cone angle varies by fishfinder model and manufacturer. Many fishfinders use
only one sonar beam; however Humminbird has advanced multi-beam sonar
technology that sends out, 2, 3 or even 6 sonar beams to cover much wider area
with much greater detail than ordinary fishfinders. Check out our sonar beam
configurations page for more information about this unique technology.

Fish Targets

Fish targets are displayed as either the unprocessed sonar return called an "arch", or
as a Fish ID symbol. You can choose either presentation.

To display Fish ID symbols, a Humminbird fishfinders use sophisticated software to
analyze the "shape" of the sonar return from a suspended target to determine
whether it is a fish. When a fish is detected it is displayed as graphic fish symbols on
your viewing screen. If you have a multiple beam configuration, Fish ID provides the
added benefit of identifying the location of the fish: either, to the left, right or
directly below your boat.

To display "arches", the fishfinder relies on the characteristics of sonar. When a fish
passes directly through the transducer's beam, it can form an arch on the display
screen. The size of the fish arch is affected by the sensitivity setting of the unit,
your boat speed, the depth of the water and the location of the fish within the sonar
beam. Often only partial arches will be displayed because the fish does not travel
directly through the center of the beam.

Water Clarity

The water's clarity also has a great deal to do with the integrity of the signal. Strong
winds or currents can create bubbles in the water that disperse the signal.
Suspended mineral particles or floating algae, plankton or other microorganisms could
absorb sound rather than reflect it back. Wave action can also stir things up - the
greater the chop, the more air gets into the equation.

Thermoclines

Some fishfinders also show thermoclines, which are the "fronts" where warmer waters
intersect with cooler waters. Typically, the water is colder as you go deeper and
certain fish prefer certain temperatures. The change in water temperature causes
some of the sonar signal to reflect back creating a line across your screen at the
depth of the thermocline. Identifying thermoclines brings you one step closer to
catching the fish you're after.

The Transducer

The transducer takes the electrical signal from your transmitter, turns it into sonar,
and sends it out. It also captures all returning echoes and converts them back into
electrical signals. Transducers are mounted in the water, either on the transom, the
inside the hull, or on the trolling motor. All transducers should be mounted straight
down and away as far from motors, props and hull obstructions as possible. A cable
connects the transducer to the fishfinder.

The LCD Display Screen

The LCD displays the sonar information and is the one of the most important aspects
of the fishfinder. LCD displays are measured in "pixels" - the little square blocks on the
screen that make up the image. More pixels provide better resolution and a clearer
picture. FSTN displays, standard on all Humminbird products, offer the best visibility
from any location on the boat, and provide high contrast for easy reading. FSTN
displays are easy to identify because the pixels are black, not blue. Grayscale
technology offers even more detail by showing the sonar image in multiple shades of
gray; this makes it easy to clearly distinguish bottom type, structure and fish.