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Chirp vs Broadband. Cone angle

Old 02-21-2015, 11:43 AM
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Default Chirp vs Broadband. Cone angle

Does anyone know why the cone angles are reversed on chirp vs traditional sonar. Chirp is lower the frequency the narrower the cone angle while traditional sonar is opposite. Is it a physics thing or by design. Makes more sense for the deeper penetrating frequency to have a narrower cone angle.
Old 02-21-2015, 11:58 AM
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In order to measure the transducer's cone angle, the power is first measured at the center or axis of the cone and then compared to the power as you move away from the center. When the power drops to half, the angle from that center axis is measured. The total angle from the -3db point on one side of the axis to the -3db point on the other side of the axis is called the cone angle. For example, a transducer that has an 8 degree cone angle at -3db would have a 16 degree cone angle at -10db.
Old 02-21-2015, 12:00 PM
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Traditional B260...low....50 kHz cone 19 degrees fixed.
Traditional B260 High...200 kHz...6 degree cone fixed.

CHIRP B175 L....40 to 60 kHz...32 to 21 degrees cone angle......not narrow at all.
CHIRP B175 M...85 to 135 kHz...16 to 11 degree cone
CHIRP B175H.....130 to 210 kHZ....10 to 6 degree cone.

They are not reversed for CHIRP.

Last edited by semperfifishing; 02-22-2015 at 10:27 AM.
Old 02-21-2015, 12:35 PM
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OK I figured it out after some more research. Someone needs to tell Navico that they have the cone angles backwards on their transducer selector tool (chirp transducers) and it does not work period on the traditional transducers.
Old 02-21-2015, 12:57 PM
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Originally Posted by popeyeiii View Post
For example, a transducer that has an 8 degree cone angle at -3db would have a 16 degree cone angle at -10db.
Huh? There is no basis for that. The bandwidth at -10dB depends on the shape of the transducer's main lobe.
Old 02-21-2015, 12:59 PM
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CHIRP B175H.....130 to 210 kHZ....10 to 6 degree cone.
I thought the b175CH had a fixed 25 degree cone. Which was a big benefit of that model.?
Old 02-21-2015, 01:06 PM
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B175H-W is marketed as constant 25 degrees constant cone angle, and it's not far from the truth.

The actual numbers are 24 degrees at 160kHz, 30 degrees at 200kHz and 26 degrees at 235kHz.
Old 02-21-2015, 01:28 PM
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Originally Posted by migrator View Post
I thought the b175CH had a fixed 25 degree cone. Which was a big benefit of that model.?
There is a B175C-H with variable cone.
And also the B175C-HW fixed cone as abbor related to.

Link to info about the HW:

http://www.thehulltruth.com/semperfi...rs-update.html
Old 02-21-2015, 01:29 PM
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Ok. I got it. Didn't know there were two variations. Thanks
Old 02-21-2015, 02:29 PM
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Originally Posted by migrator View Post
Ok. I got it. Didn't know there were two variations. Thanks
With all the different transducer options..hard to keep up .
Old 02-21-2015, 04:45 PM
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Originally Posted by semperfifishing View Post
With all the different transducer options..hard to keep up .
Yea especially when the manufacturers give very little if any info on real world applications.
Old 02-21-2015, 04:56 PM
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Originally Posted by semperfifishing View Post
Traditional B260...low....50 kHz cone 19 degrees fixed.
Traditional B260 High...200 kHz...6 degree cone fixed.

CHIRP B175 L....40 to 60 kHz...32 to 21 degrees cone angle......not narrow at all.
CHIRP B175 M...85 to 135 kHz...16 to 11 degree cone
CHIRP B175H.....130 to 210 kHZ....10 to 6 degree cone.
Gil, excellent and straight to the point.

However, could you take it one step further and add the ideal fishing depths to each line.

In other words just add B175L would be ideal for those fishing in depths XXXft-YYYft.

I know that's going out on a limb for you because some might argue so anything you could provide would be much appreciated.
Old 02-21-2015, 05:29 PM
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Its been stated that the b175hw, gives excellent results under 300feet and continues to give great results to 600/800 feet in salt and to 1200 in fresh waters, litteraly pulling fish off the bottom!
The Narrow cone angle of the b175h would be better for a fisherman looking to pinpoint holes.
B175L would be best for deep dropping and for work past the range of the H.
The B175M is best for 300feet to roughly600/800feet
Remeber that water conditions effect a transducer. What may be an ideal setup on the East Coast my not be on a muddy murky river or on the West Coast. What works for Salmon wont be ideal for Tuna, Swords, etc. There are many variables to go into the selection / recommendation of a transducer.
I hope this helps

Last edited by BoemarineBrian; 02-21-2015 at 05:46 PM.
Old 02-21-2015, 06:07 PM
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Originally Posted by Lima Bravo View Post
Gil, excellent and straight to the point.

However, could you take it one step further and add the ideal fishing depths to each line.

In other words just add B175L would be ideal for those fishing in depths XXXft-YYYft.

I know that's going out on a limb for you because some might argue so anything you could provide would be much appreciated.

Selection of a transducer is helped by considering the transducers paramaters..

The high band transducers have greater small target detection capability...but due to the shorter wave length.. far less energy available to obtain great depths.
Add to this the narrow cone angle of high band units....good bottom detection due to a smaller cone.
The exception is the 25 degree HW..at a fixed 25 degree cone only marginal bottom detail, but due to its higher quality element specific to this ducer..one of the best for small target detection under 300'.

The Low band units have a much longer wave length.. and thus far more energy available to achieve greater depth.
But the longer wave length has less capability to detect smaller targets..but excellent for deep bottom reading.


So the medium bands give us an excellent compromise...between depth and small target detection...and is a choice of many who's fishing takes them thru a range of depths from shallow to deeper ranges.lets say down to 700' or so for targeting.

Add to this ..the number and quality of elements plus using single or dual band transducer.

Looking at targets deeper than 1000' require a 16 or 25 element unit.... in the medium and low bands.

So no really simple answer..but understanding the basics helps.
Old 02-21-2015, 08:22 PM
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Great info. Thanks to both Brian and Gil.
Old 02-21-2015, 09:43 PM
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Originally Posted by Capt. Steve Barnes View Post
Makes more sense for the deeper penetrating frequency to have a narrower cone angle.
I agree 100%

I tried to get to the bottom of this when researching for my latest book, but came up empty handed.

The question is - Is it a design error, or simply a technology restriction?
Old 02-21-2015, 10:36 PM
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Originally Posted by Fishton View Post
I agree 100%

I tried to get to the bottom of this when researching for my latest book, but came up empty handed.

The question is - Is it a design error, or simply a technology restriction?
It is not a design error or a technology restriction. It is the physics of sound wavelengths, that's what the above posts are trying to tell you put simply.
Old 02-22-2015, 03:23 AM
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If the size of the transducer element is constant a lower frequency will give wider cone. If the frequency is constant a larger size element will give a narrower cone.

So to get a narrow cone at low frequencies a very large element or a large array of smaller elements are needed. This gives a very large and very expensive transducer (ex: R399)
Old 02-22-2015, 09:28 AM
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My head hurts. Glad someone else pays attention to this stuff.
Old 02-22-2015, 09:29 AM
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Originally Posted by Nomans View Post
It is not a design error or a technology restriction. It is the physics of sound wavelengths, that's what the above posts are trying to tell you put simply.

You sound like my grade 5 maths teacher 'Normans' - I failed miserably as a result of her 'style' of teaching.

However, in high school I got a teacher much like abbor, with clear simple instructions, and ended up doing very well as a result.

This makes total sense -
abbor - "If the size of the transducer element is constant a lower frequency will give wider cone. If the frequency is constant a larger size element will give a narrower cone.

So to get a narrow cone at low frequencies a very large element or a large array of smaller elements are needed."

That is why side sonar uses such long elements I presume?

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