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Transducer Cone Angle

Old 02-11-2012, 05:41 PM
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Default Transducer Cone Angle

I've been reading up a little on different transducer frequencies and cone angles. What doesn't make sense to me is the 50khz always has a wide beam and the 200khz has a narrow beam. If 50 khz is best for deep water and 200khz is best for shallower water wouldn't it make sense for that to be reversed? Can someone explain that to me?

Gary
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Old 02-11-2012, 05:57 PM
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I guess you answered your own question...because 50kHz is a lower frequency than 200. I.E. ,a foghorn (lower frequency) travels farther than a whistle(higher frequency).
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Old 02-11-2012, 06:21 PM
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The main issue sonar deals with is wave length.

The 200 kHz pulse being shorter does not have a great deal of energy and therefore cannot penetrate very deep...but it is able to give more detail.
If you have too wide a cone at 200 kHz then there is not enough energy left for reasonable depth.

The important factor with sonar is wave length.
A sound wave needs something larger than itself in order to get a return echo.
If the target is smaller than the sound wave than the return echo will be very weak.

Take the speed of sound in water...4800 ft/sec divided by 200,000 cyc/sec = .024 Ft/cyc = 0.29 inches/cyc

That means one sound wave from a 200 kHz transducer is slightly longer than 1/4 of an inch. That means a 200 kHZ signal can detect fish with bladders as short as 1/4 of an inch.
The 200 kHz signal being a short wave length does not have the energy to penetrate deeply but its able to have greater detection capability.

the 50 kHz wave length being longer has more energy and can travel far deeper..but is less sensitive to smaller targets.

A 50 kHz sound wave is over an inch long and will only detect fish with larger bladders.
But it does have the ability to read bottom structure at great depths.

So...transducer designers have to keep the cone angle of the 200 Khz elements narrow because if they get too wide then there is not enough energy left for any reasonable depth.

They can give far wider cones to the 50 kHz side because it has longer pulses and thus greater energy.

Always a compromise.

Last edited by semperfifishing; 02-11-2012 at 06:42 PM.
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