cone angles

[PFUNK]

So I just bought a new sonar from a fellow HSOer (thanks perchjerker) and am curious as to other's experience with it. It is a Humminbird ICE 385ci. I went with this model because I was looking for something that could be used ice fishing and then on open water. The one thing that worried me most was that the dual transducer has 20/60 degree cone angles. I was a little worried that the 20 degree ducer would be too wide to pick up small jigs when fishing 30+ feet of water. But I read some other forums and heard that some guys use the 19 degree cone on their flashers 90% of the time anyhow. Has anyone used this unit that can give me some tips on how to maximize its performance. Do you have to crank the sensitivity way up to be able to pick up your jig? Do weeds make it even tougher? Does a hard bottom help? Stuff like that. Any tips or advice is much appreciated. Thanks.

[heat checker]

I just got same unit for xmas,used it a half dozen times or so. Not much experience with it yet, but I seemed to have the best luck on the 200/83 setting. I set the sensitivity as low as it would go, then increased it until I had good response to my jig. I believe I stopped at about "10" fishing in 20fow with a tiny sunfish jig. Hope to here from others with more experiance with this unit also.

[PFUNK]

Heat checker... the sensitivity goes up to 20 right? So I would think I should be able to fish 30 feet of water without problems picking up a jig. I noticed the unit has a great power rating of 2400 watts peak to peak so I was hoping that might help make the 20 degree cone penetrate a little deeper than it would on a unit with lower power. Have you used the zoom feature at all yet and do you normally fish with the flasher screen or the scrolling sonar?

[My_Key]

I'm not sure if I understand your original post or not. It seems like that you think the 20* cone is too wide for deep water? Since the unit you bought is an ICE series, the concept of picking up the jigs in deep water should have been well thought through by the Humminbird engineers. At 30 feet down, your 20* cone has a diameter of roughly 10 feet. If your ever wondering how much area your cone is covering at any time with a 20* transducer, just divide the depth by 3.

[PFUNK]

Yep you got it right. I am concerned that a 20* cone may be too wide for picking up tiny little sunfish jigs or vertically hanging perch jigs at 30+ feet. A lot of your typical flashers come with cone angles of 9* or 12* which concentrate better and can pick up a jig with ease. My dad uses a 9* transducer which can pick up a bobber stop or bead on the line in over 30 feet. I just want to be sure I will be able to get this same performance out of a 20* transducer. Also, how much does the units power rating come into play? I have a fairly powerful unit with a rating of 2400 watts Peak-to-Peak. I am hoping this might help make that 20* cone penetrate better into deeper water. Is that correct? I am under the presumption that narrower cones with higher frequencies can show more definition of the bottom but are limited by their depth penetration. Whereas wider cones (60*) operate at lower frequencies and can penetrate deeper but show less definition. One final question. Can someone please explain how these companies rate their cone angles? For example, my Humminbird unit says that the 200 kHz frequency produces a 20 degree cone at -10dB. A lot of other companies measure their cone angle at -3dB. So I guess I am wondering what the cone angle would be on my 200 kHz sonar if it had been measured at -3dB like some other manufacturers do. Would that make it wider than 20 degrees or would it tighten the cone up to something less than 20 degrees? Hope this isn't confusing. If it is let me know.

[My_Key]

One final question. Can someone please explain how these companies rate their cone angles? For example, my Humminbird unit says that the 200 kHz frequency produces a 20 degree cone at -10dB. A lot of other companies measure their cone angle at -3dB. So I guess I am wondering what the cone angle would be on my 200 kHz sonar if it had been measured at -3dB like some other manufacturers do. Would that make it wider than 20 degrees or would it tighten the cone up to something less than 20 degrees?

This changes everything. the -10db rating means they are calculating the cone angle at 1/10th total power, whereas the other manufaturers are calculating their cone angles at half power (-3db).

Essentially, measuring at -3db instead of -10db tightens up the cone angle. Your "20-degree" is probably not all that different from your dad's 9-degree. I'm sure there are charts somewhere that show the difference.

[Norm1980]

I currently have the 345c which i have used the past two years (same unit with out gps). I got it for the same reason you did because i can use it in summer and winter. I have been happy with the unit on the ice, i would say the only down fall i have seen so far is when fishing a hard bottom (rocks) around a vexilar (fl8's seem the worst) you will get a decent amount of distortion.

Otherwise I have been in as deep as 38' and not had one problem seeing my jig right on the bottom. I use the flasher screen on the ice because you can adjust your dial so you can zoom in on any depth in the water column. I usually have my sensitivity around 8. Battery life is good, I have not had a problem going on 3 day trips and having to re-charge.

For summer the unit also has worked well. I did not like the portable transducer as the rubber suction cup has all but fallen apart on me do to exposure to sun/water(bought a perm mount). The screen could be a little bigger, I plan on switching mine to the front of the boat by the trolling motor when i have enough money to purchase a bigger one for the back.

[PFUNK]

Thanks for the info Norm. That is a relief to hear you have been that deep and haven't had any problem picking up you jig. Did you still get a lot of interference after using the noise rejection feature or didn't you try it? The small screen is one thing that bothered me as well, but when you are on a limited budget there isn't much else you can do.

[toddb]

Technically -3dB is not half power and -10dB is not 1/10th power. Starting with a known target set at a reference level using the nominal beam angle (0 degrees). To measure beam angle this way A gain reduction of 3dB will reduce the amplitude of a returned signal to 71%, 6dB will reduce the amplitude of a returned signal 50% and 10dB will reduce the signal amplitude to approximately 31% of your reference amplitude.

Now for measuring, move the target from the reference location until the amplitude is reduced to 31% of the original value. This distance from reference would be the 1/2 angle beam spread for your cone(measure the distance from reference and calculate the angle with the 2 known legs of the triangle using trig functions).

I work in industrial Ultrasound and typically we use +/-6dB calculate beam spread. Not sure why HB uses 10dB for measurement as sound field intensities can vary greatly at further distances especially when you get to the point where the beam really starts to go away(Far field). It is probably a marketing thing to not sound like the others when in reality there transducers are probably doing the same thing.

In reality if they are saying the have a 20 degree cone at -10dB your echo strength at the edge of the cone where beam intensities are considerably less is going to be much smaller than a 20 cone measured at -3dB. I am assuming you have a dual beam option and a lower frequency option which would give you a much broader cone alll things considered. True beam measurements in ultrasonics are much more affected by the aperture (size) of the transducer and Frequency of the transducer http://www.ndt-ed.org/GeneralResources/Formula/UTFormula/BeamSpread/BeamSpread.htm.

[PFUNK]

Thaks for the post Todd. You sure sound like you know your stuff. I am understanding it more and more but it is still a little fuzzy. Basically what I am getting is that Humminbird measures the "edge" of its cone as the point where 69% of sound intensity has been lost as compared to the point of greatest intensity (directly under the trasducer). In comparison, a company who measures its cone angle in terms of -3db defines the "edge" of its cone as the point where 29% of the sound intensity has been lost. I think the definition of "cone angle" can be very arbitrary then as all these companies have different ways of measuring it. Is there a mathematical formula I could use to figure what my cone angle would be if it had been measured at -3db compared to -10db. Or would I actually have to measure how far out from the side of the traducer beam I must move until the sound amplitude decreased by 29%. I would also have to know the distance below the transducer that this reading was taken and using these two measurements I could find the hypotenuse to the triangle and using trig find the angle as well. Sure would be nice if all these companies would agree to measure the angle the same way wouldn't it?

[heat checker]

PFUNK... not to jack your thread on the ducers, but have you looked at what it will take to mount in boat? I was going to do that today, ended up not getting done. The way it looks, will need another quick release mounting bracket, and can't tell if the power lead and transducer lead come with it by the pics. Maybe you've got it all figured out already? If so, let me know what you came up with.

[PFUNK]

PFUNK... not to jack your thread on the ducers, but have you looked at what it will take to mount in boat? I was going to do that today, ended up not getting done. The way it looks, will need another quick release mounting bracket, and can't tell if the power lead and transducer lead come with it by the pics. Maybe you've got it all figured out already? If so, let me know what you came up with.

Yeah I have looked into this. You need 3 different accessories. I decided on the transom mount transducer (Part number: XNT 9 20T $67.99), the boat mount (MS M $32.99), and the power cable (PC 10 $13.99). If you need anything else let me know. All the accessories are on HBird's HSOforum and if you click the contact Humminbird button you can ask them questions and they get back within 1 or 2 business days.

[Norm1980]

Did you still get a lot of interference after using the noise rejection feature or didn't you try it?.

I did mess with the noise rejection and it didn't seem to help much, i usually leave it on High1 with Sensitivity any where from 8 to 12. I have only ran into trouble with interference when fishing deeper water with a hard bottom (rocks/gravel). when fishing mud/sand or shallow water I have not noticed the interference. Thus is my experience from fishing in a 8x16 ice house with two other people both using vexilars (fl8 & fl12). The vexilars also experienced some interference so it wasn't just the humminbird.

[PFUNK]

Well I guess nothing can be perfect. I have heard that the Humminbird's typically don't get as bad of interference while fishing close to other sonars as most units do like Vexilar or Marcum.

I

was able to find a really nice explanation of sonar's and cone angle on Lowrance's HSOforum. I am not going to post a link because last time I did that my account got suspended for a few days. Didn't intend to do anything against policy but I guess I did. SO just google search "Sonar Tutorial Lowrance" and click on the first link. It should be Lowrance's HSOforum. Anyhow, the section on transducer cone angles seems to suggest that to convert from a -3db to a -10db measurement, you simply double the cone angle. So an 8 degree cone measured at -3db is the same as a 16 degree cone measured at -10db. Therefore, my Humminbird 20-degree cone would be equal to a 10-degree cone measured at -3db. Exactly what I wanted to hear.

[toddb]

Pfunk,

There are way too many variables involved in ultrasonics when you get down to it. Amplitude drop is one way of measuring your leading and trailing beam angles, but there is no formula to measure it accurately. You would just be interpolating between 2 knowns. When we measure beam spreads it is usually done on known reflectors, which is the most accurate way.

Alot of industrial sound field measurements are done with software that measures the sound field generate based on essential transducer, pulser, and specimen(water) variables. One can measure sound fields generated based on the physics of your system- itcan be determined by calculation. Usually thats where we start with technique development. The laws of physics are usually pretty right, but actually physically verifying that your technique works is a good thing. I am pretty sure the companies that produce the equipment do their fair share of testing also...

With the low frequencies used with fishing sonar it amazes me that these units that are sold for 200 to500$ can see great detail up to 100' deep and greater.