Horizontal beam width and resolution, the HB silence.

[Rickard]

Hi,

I have, without success, tried to get confirmation on my estimates of beam widths for the various Humminbird sidescan transducers. The manuals for the SI 700, 900 and 1100 models tells a lot about beam angels in many directions for many frequencies but NO manual reveals the most important figures for the horizontal beam widths for sideimaging. This is most frustrating and gives a bad feeling that HB has decided not to reveal these specifications. My own estimate is 1.4 degrees at 455 KHz at - 3dB for the transducer for the 981 model. Since this is not very impressive at that frequency I suspect this explains HB's silence. But extremely narrow beam does not need to be the best for fishfinding. Too narrow beam could actually be bad for fishfinding since then the fish could appear as too tiny dots on the screen. Most members of this forum have, I think, other purposes than fishfinding in mind (like wreckhunting) and thus they want the narrowest beam width possible. I think it would be very, very good if HB could sort these is issues out and tell the forum the true figures for beam widths and explain why there might be reasons for not using the narrowest possible beams for fishfinding. Further, I think there is a market for a transducer for the sideimaging units with much better (narrower) beam than those provided by HB today. Actually, since the present tranducers seem to work as fishfinder transducers always have been working (high voltage output from the instrument and no signal processing in the transducer), any reasonably handy person could make his/her own array. A 300 mm array could produce a - 3dB beam, 0.5 degrees wide at 455 KHz. That would be really narrow.

Regards with some frustration... and admiration of HB's products!
Rickard

[rgecy]

I have dealt with the guys at Humminbird and found them to be very friendly and great to work with. They are very much in to customer satisfaction.

But, I also know they are very secretive and want to protect their technology edge in the market right now. I don't blame them.

I have read somewhere where the beam angle was around 1.5 degrees. Yes, thats not impressive in comparison to the $30k + units on the market, but it is impressive to fit 1.5 deg into that little transducer.

So, I know they have an awesome engineer who used to work on naval sonar systems. If it can be done and is in the Humminbird business plan or product model, he can do it. My opinion is, that there is very little interest in a larger transducer, even though it may provide better resolution.

Can you build one that will work with the unit?

Robert

[Rickard]

Yes,

I think I could build one. Provided there is time for it and I could find a supplier of 455 KHz piezos. These are very narrow bottlenecks which probably will keep me from ever proving my bold statement...

I know the people at HB are very helpful. They gave me many tips and facts during my early Matrix 37 period. Perhaps I was in too bad temper when I wrote my post. It did not mean to insult or question someones competence. I was simply frustrated. It's better now.

Although the HB SI machines are wonderful I think they still have an unused potential. 455 and 800 KHz (that's high), high-definition screen and, thanks to you, support for analyses on PC, is an incredible situation compared to just a few years ago. We should be thankful. And we are. Just a little longer arrays (up to 400 mm) and there will be no difference in resolution left between HB:s units and 'professional' systems. Professional systems will still be the only alternatives for large depths but in shallow waters the HB will be as good. But you may be right, the number of people who will pay the extra cost is probably not high enought.

I stumbled over a few screenshots on the net showing results from a HB 981 and a Hultqvist 200 KHz system. Some wrecks have been scanned with both systems. It's interesting to have opportunities to compare results showing the same targets. I think the 200 KHz system has a 0.8 degree beam. http://www.wern.com/id13.html

Rickard

[Rickard]

Length of transducer?

Does anyone know the length of the transom Humminbird HDSI transducer XHS-9-HDSI-180-T? This is the one used for the 990 and 1100 models and operates at 455 and 800 KHz in sidescanning. Asking because length sets the limit for resolution and no data on resolution are presented in the manuals.

Rickard

[Seaklod]

Dear Rickard,

I am still trying to figure out how exactly a sidescan sonar works (fish, amplifier and trigger, piezo receiver, data processing, etc.). Internet is of course a good source of learning and I particularly like your posts and experiments. In this thread, you said that the length of the transducer sets the limit for resolution. Is it possible to explain this concept in a few phrases?

Or maybe answer my larger question : why the use of an array of transducers insted of a single source? Is it a cluster to gain power and sensibility? Or to produce a geometric wave patern for accuracy or something? Or a longer transmit/receive "train" in order to still catch the echo at greater speed (which could explain why the array oriented in the boat axis)?

Thanks for your time.
Sylvain

[Rickard]

Hello Sylvain,

Sorry for my late response but I have been out for a week on a boat trip in the archipelago.

It’s not so easy to give short answers on your questions. I don’t know all the answers myself and the areas of SONAR and RADAR are really complex engineering sciences. However, the basic laws controlling beam forms are rather simple. All you need is an understanding of wave theory and some mathematics. It’s impossible to explain the rest in a few words here. I suggest you take a look at the course material at this place:

http://www.omg.unb.ca/GGE/SE_3353.html

The material consists in a large set of PowerPoint presentations but they are still rather easy to follow. The slides on “Angular Resolution” are the most central to us. Many piezo manufacturers have texts on their sites where the principles for beam forming are explained. But the rules-of-thumb are; the longer the transducer and the higher the frequency, the narrower the main beam. A transducer could be a continuous object but sidescan transducers are made up of separate elements forming arrays for practical reasons. It’s simply too difficult to produce piezos that long. In more advanced systems (shading and beam steering) separation in elements are needed though.

Regards.
Rickard

[Seaklod]

Thank you so much for your time. This is exactly the kick start I needed to make some sence in all this and understand the basic jargon. I just took a brief look at the PPT files and it looks promissing.

Hopefully, I will be able someday to make some contribution to this forum.

Thanks again,
Sylvain

[UWLocator]

HB Patent Application

There is a lot of info on the transducers in the patent application. See US patent application 20060023570 for details and drawings.

Rip

[UWLocator]

The patent application states that the beam width is about 2 degrees. However, the application covers the lower frequency side scan. I have not seen one that covers the newer 800kHz units.

Rip

[Rickard]

Patents

Thanks,

I wonder why I didn't think of searching for the patent after all that talk about a HB patent that prevents all other fishfinder manufacturers from presenting competing products. The figures and drawings are interesting indeed. They confirm much of what have been guesses and indirect inferences until now. I think the figures on beamwidths are provisional and they don't tell the dB level or the frequency in the application text. They say the length of the sideimaging element is about 4.5" which is what you estimate if the length of the flat surface is measured. This yields a 1.4 degree beam at -3 dB and 455 kHz. I couldn't find a filed patent so it looks as if the application wasn't approved? But Dave Betts and his collegues have some other filed patents (e g the Smartcast and control of sidebeam ping rate based on downlooking depth reading) on principles used in the SI transducers and the sideimaging systems so the transducer is probably well protected anyway.

Rickard

[UWLocator]

Thanks,

I wonder why I didn't think of searching for the patent after all that talk about a HB patent that prevents all other fishfinder manufacturers from presenting competing products. The figures and drawings are interesting indeed. They confirm much of what have been guesses and indirect inferences until now. I think the figures on beamwidths are provisional and they don't tell the dB level or the frequency in the application text. They say the length of the sideimaging element is about 4.5" which is what you estimate if the length of the flat surface is measured. This yields a 1.4 degree beam at -3 dB and 455 kHz. I couldn't find a filed patent so it looks as if the application wasn't approved? But Dave Betts and his collegues have some other filed patents (e g the Smartcast and control of sidebeam ping rate based on downlooking depth reading) on principles used in the SI transducers and the sideimaging systems so the transducer is probably well protected anyway.

Rickard

In the detailed description, they give the preferred frequencies of 260kHz and 462kHz. They also state that the beam angles are 2 degrees and 50 degrees. If memory serves, HB uses the -10 db points for most of their specs, so that may be the case here.

Rip

BTW, it is still an active application so it could yet be approved at some point. I suspect that the examiner has raised issues that they have to address to continue the process.