Understanding the basics of a Fish Finder can help anglers fill their live wells, win tournaments, and keep their boats away from places hazardous to the health of props, lower units and boat hulls.
Fish finders can’t find fish. "They can only tell you when you have found fish.” your fish finder is only as valuable as the amount of time you invest in learning how to use it and using it. If properly installed and functioning it will produce a wealth of information for any angler. Fish Finders work by sending an electrical impulse from the transmitter, converting it into a sound wave by the transducer and then sending that sound wave into the water. It is a Sonar. When the wave strikes an object it rebounds off the object sending an echo back to the transducer. The transducer then converts the echo back into an electrical signal. The receiver amplifies this signal and sends it to the display for you to see.
The Basics of Depth Finders Fish Finders │ Installing a Fish Finder │ Questions & Answers About Fish Finders │ Fish Finder Glossary of Terms
Fish Finders have 4 basic parts.
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Transmitter
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Transducer
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Receiver
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Display
The Computer:
A small amount of current from your battery is taken by the transmitter of the depth finder and converted into pulses. The computer sends these pulses to the transducer. The computer will continue to tell the screen to light up pixels as long as an object stays in the cone. With this in mind the length of an object on the screen, such as a Striped Bass, has nothing to do with the size of the object. A Striped Bass swimming in the same direction of the boat will stay inside the cone for a long time and produce a long thin line on the screen. A thick mark, no matter how long is a strong signal, i.e. harder bottom or a bigger fish.
The Transducer:
As the pulses from the computer reach the transducer, they are modified, being changed from electrical impulses to sound impulses. The transducer sends out these sound waves at regular intervals and “listens” for their return after they bounce off the bottom. Sound waves that the transducer produces move downward in the shape of a cone. Most transducers have a 20 degree cone angle. A 20 degree cone angle will show you approximately 10 feet of the bottom in 30 feet of water. Sound waves in water travel away from the transducer at about 5,000 feet per second. When they strike an underwater object or the bottom, they are reflected back up to the transducer. Called “echoes”, the reflected sound waves re-enter the transducer where they are converted back to electrical impulses.
There are two basic transducers, Low and High frequencie. Low frequencies range from 50 to 100 kHz. High frequency models from 180 to 200 kHz.
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50 kHz |
200khz |
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The Screen:
The returning echoes are then run through an amplifier to
make the impulse signal stronger. Next the computer measures the length of
time it took for the signal to return. The speed of sound waves travelling
through water is a constant so the exact depth of the water can be
calculated. The computer takes that information and sends it on to the
screen. The screen lights up small squares called ‘pixels’ so you can view
it. Pixels are arranged in a grid pattern on the screen. The screen is a
certain number of pixels high and a certain number wide. The number of
pixels in width is important to the amount of bottom “history” you can see
on the screen and the vertical number of pixels is critical to how much
resolution the unit offers.
So how much resolution is enough? Less expensive depth finders have 100
vertical pixels while the high-end units offer 240 or more. Let’s compare
the two.
In 40 feet of water, a depth finder with 100 vertical pixels, 1 pixels
equals 4.8 inches. If a four-pound walleye was inside the cone, 1 pixel
would light up to represent its girth. So a walleye within 5 inches of the
bottom would blend in with the bottom on the screen. On the depth finder
with 240 vertical, each pixel equals 2 pixels, so the same walleye would
light up 3 pixels. Since more resolution can be shown, the same walleye
would be a slight bump on the same bottom.
Operation Tips:
Tip #1 - With that said the quickest way to learn how to operate your depth finder is to leave your rods at home. Go to a clear lake where you can see bottom to at least 10 feet. Simply compare what you can see visually with how your depth finder reports it. If you can see rocks, watch how your screen records rocks. The same applies to detecting weeds, brush, and even the bottom. This can accelerate your learning process by years.
Tip #2 - Do not use the Fish ID feature! This option draws precious power by making the unit interpret the signal for you. Learn to recognize fish by the arcs and you’ll be much better off.
Tip #3 – With most units the sensitivity or gain control is an automatic feature. The computer interprets the information it receives and adjusts the sensitivity up or down, to give you the clearest picture possible. To get the most from your unit put the sensitivity in manual. Now slowly turn the sensitivity up a little until a second echo or false bottom reading appears on the dial. (The second echo should appear on the dial at twice the actual bottom depth.) When that second echo appears, the unit has been fine-tuned for sensitivity to mark everything between the transducer and the bottom, including tiny minnows, weeds, brush and, of course, walleyes.
Tip #4 – Walleye are bottom - hugging fish so use the zoom feature. This option will give you a more detailed view of where the ‘eyes’ hang out and allow each pixel to represent more detail.
Tip #5 - When marking fish on your depth finder, don’t try to determine what type of fish it is. Consider every fish a walleye and fish it with confidence and determination to make it bite!
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