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Old 10-15-2011, 06:03 PM
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Each frequency has its own particular advantages.

200 khz gives better detail, shows less noise and undesired echoes. Also, target separation is better with the higher 200 kHz frequency.
Waters absorption rate is greater for higher frequencies and shorter wavelength thus a 200 kHz sound wave will have less depth penetration than a 50 kHz signal.

50 kHz sound waves can penetrate far deeper due to the longer wavelength.
thus they will penetrate deeper but also will have less definition and target separation.And 50 kHz sound waves will have greater noise than a 200 kHz signal.

So it boils down to:

200 kHz
Shallower depth
Narrow cone angle
Better definition and target separation and less noise.

50 kHz

Greater depth
Wider cone angle
Less definition and target separation and more noise.

But used together on a split screen , each adds to the overal sonar picture so the fisherman has a wide variety of information of conditions and targets under his keel.

And some sonars such as the Furuno FCV620/FCV585 have the ability to help the user locate the target by utilizing the different frequencies and their respective cones.

When using either of these units if you read a depth number right on the target that means the fish in within the 200 kHz cone.
If you still get a great target but no depth number on the target the fish is outside the 200 kHz cone width but within the 50 kHz cone.

This fish target is inside the 200 kHz cone. Being that this is a 12 degree cone the width at 113' is 24'..this fish is basically under the boat.

Same target but now outside the 200 kHz cone but still within the wider 50 kHz cone. This being a 45 degree cone the width at this fishes depth is 94' wide.

Now you know that the fish is port or starboard and not under your you make a 360 until you pick up the target with a depth number on it..then it is under the boat.

Last edited by semperfifishing; 10-15-2011 at 10:09 PM.
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