20 degree transducer view

I have a humminbird with a 20 degree transducer,the cone is 20 degrees,If im in 20 feet of water,how much of that bottom am I really seeing.Im told its about 1/3 of depth,so that means im only seeing about a 6 ft. circle right below my boat. Am I correct in that asumption.And what is the actual coverage with some of the newer locators,To me a 20 degree cone is a 20 degree cone I know there is different power levels and you might get some over the actual cone coverage rating. but alll in all how wide does some of you guys locators cover under your boat...

This may help explain the difference in 2D, Down Imaging,and side imaging sonar units and transducers. There are also lots of other videos on youtube explaining sonar cone, etc. With side imaging you can cover the size of a football field. Although I keep mine set on 40' to 60' to be able to know what I am seeing better. I am using a Humminbird 899ci HD SI unit and I am really liking it so far.

https://www.youtube.com/watch?v=_FYMWCyhTpI

https://www.youtube.com/watch?v=yQIVru6xHGk

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Originally Posted by helpme

I have a humminbird with a 20 degree transducer,the cone is 20 degrees,If im in 20 feet of water,how much of that bottom am I really seeing.Im told its about 1/3 of depth,so that means im only seeing about a 6 ft. circle right below my boat. Am I correct in that asumption.And what is the actual coverage with some of the newer locators,To me a 20 degree cone is a 20 degree cone I know there is different power levels and you might get some over the actual cone coverage rating. but alll in all how wide does some of you guys locators cover under your boat...

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If you are referring to a 20deg cone of a 2d sonar unit .... you are correct !! The diameter of the circle on the bottom would be a little over 6.5ft wide (and taper smaller as it's measured upwards to the transducer). That's usually a 200kHz frequency.

An 83kHz frequency will put out a 60deg cone, which will have a circle on the bottom that's equal to the depth ... so in 20fow the diameter of the circle would be 20ft wide.

Down Image and Side Image units don't create "cones", they create thin slices of about 2-3deg width. Their sonar pings are fan shaped, and use the 455kHz & 800kHz frequencies. Side Image units cover almost 180deg, while Down Image units cover 45deg & 75deg angles (depending on which kHz setting is used).

http://i826.photobucket.com/albums/z...newDIbeams.png

There are 2 advantages to the smaller 20° Sonar cone ...

1. Better detail due to higher frequency sound pulse ...
2. Fish showing on the display are most likely near directly under the xducer ...

There may not be as many echoes showing as a wider 60° Sonar cone but fish under the xducer are more likely to be caught than fish in the 83kHz 60° Sonar cone...where you don't know where they are ...

Rickie

This is on an older tracker pro 128 DX locator,was thinking about an 83khz transducer but Ill just use it like it is till I can up grade to a better one. Im thinking I will use it to locate the holes and contours on the bottom. Now that you guys explained to me how these work,I have a better Idea where to drop my bait at,after all thats what these things are for,where to put your bait where you will most likely get a bite.thank you guys.....

Remember that the edges of the cone aren't sharp. There is virtually no difference in the returns from an object just outside the cone or just inside it. The cone angle just defines the point where the power is half of what it is at the center. You can still get returns way out beyond the 20° point

I didnt realize that the area of coverage was that small for that 20 degree cone,but next time im on the water I will remember that and start focaseing on just the small area where my transducer is.then use the trolling motor to locate the depressions, and dropoffs where the fish might be located, just realized if under the boat at less that 10-12 feet the coverage is only about 1-3 foot. but a shad school should show up..looking forward to see what that looks like....