# Transducer cone angle

Discussion in 'Fishing Electronics Review' started by rocket256, Sep 19, 2006.

1. ### rocket256Well-Known Member

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1,608
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Oklahoma
Name:
McGill
I have seen it somewhere, If I could remember back where I seen it I would not have this question. If your transducer has a cone angle of say 20deg how do you figure out how large a circle you are looking at in say about 20ft. of water

We all know basic trigonometry formula of a cone is:

(1/3b)(h) = V

Ok; if so all I know is the (h) which is 20ft.

Total angles of a Triangle = 180 degrees, 20 is at the botttm of the boat, 90 is straight down; that leave us with 70 left.

A 20deg. cone angle will show a circle that is 1/3 as wide as the depth. So in 20 ft of water you have a FOV (field of vision) of a lil under 7ft. Am I right?:roll_eyes:

Messages:
524
State:
Ohio
I got 7.06 feet, so your way is close enough for me and alot easier without a calculator:lol: .

If anybody wants the trigonometry lesson, I'll scan my paper, but the copier is along way off.

3. ### rocket256Well-Known Member

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1,608
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Oklahoma
Name:
McGill
Ok; cool. For a mim there I thought my math was off cause that surface area seemed so small. But; I guess I was right after all.

4. ### blackwaterkatzActive Member

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3,659
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Andrews, SC
That sounds about right, Rocket, but keep in mind that you can actually read targets that aren't in that 20 deg cone, you can actually read to about 60 deg with most units, but the signals won't be as strong, depending on how your sonar is set (sensitivity, chart speed, ping speed, etc). Per Lowrance:

5. ### rocket256Well-Known Member

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1,608
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Oklahoma
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Wow; I didnt know that. So the Lowrance X135 can be set for 60deg? If so how do you do it?

6. ### onlyriverfishMember

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319
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Name:
james
Good Question.

Like Tommy said is right. Also-raise sensitivity high as possible (screen clutter is trade-off) will give widest bottom read. If your looking strickly at-near bottom then you can stand quite a bit of cluttter raising sensitivity and still have a good bottom read.

Anyone of us could do some simple testing using object hung off sides, front, back of boat. Also lookup "DOC" post here on boc. At his web site-think he said he did this(?).

Hard to justify when ya cant get enough fishing time as it is though!:big_smile:

7. ### blackwaterkatzActive Member

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3,659
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Andrews, SC
No, that's not what I meant. You can increase the sensitivity to get a wider effective cone angle, but as I said, the signals won't be as strong. Since the x135 is grayscale, you would have to look a little closer maybe. I had an eagle fishmark 480 and could see my bait on bottom at the front of my 17' boat in 25 - 30' of water, so I was reading beyond the 20 deg coverage. With the lowrance x107c, I can't do that because of the narrower cone angle (12 deg vs 20 degree). I just installed a 20 deg transducer in addition to the original, so I can get wider coverage, but haven't been in the water yet.
For more info, go to http://www.lowrance.com/tutorials/sonar/sonar_tutorial_01.asp and click on "cone angles" on the left side of the page. It will explain what I'm trying to say. You can learn a lot from the tutorials on that page.

8. ### Mr.TActive Member

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2,554
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MO
This is about the best tutorial on sonar that I've found - read it slow so it all sinks in, and it'll change the way you think about what the sonar is showing you.

http://www.hightechfishing.com/other/Lowrance_Tutorial.pdf

You can also get a *lot* of other great sonar information if you go to the main page on the website above and follow some of the links there.

9. ### blackwaterkatzActive Member

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3,659
State:
Andrews, SC
Yeah, Marty, I've got that one on my computer. It is the best for deciphering what you see on the screen. The other link I posted is a more current version that explains the basics pretty good, but the one you posted goes into a lot of detail about reading the sonar.

10. ### rocket256Well-Known Member

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1,608
State:
Oklahoma
Name:
McGill
Thanks for all the info!