Results with home built side-scan

[Henrik]

Hello,

Here are two samples that I shot yesterday with my homebuilt side-scan.
It uses 6 pcs lowrance 20 degree / 200 kHz transducers with paralell connection. As you can see there is some optimizing to do still...

Unfortunately I was impatient enough not to let the glue dry enough so I got a leak in the fish, but I think the transducers were not damaged.

Its so much fun to see that the theory works in practice!

Henrik

[mobilegps]

hello henrik,

what fish finder did u use? how do u postition the transducer?

regards

[Henrik]

Hello again,

I use the Lowrance LMS-480, which has built-in GPS and memory card recording.
Great features with ping speed adjustments aso.

For the positioning of the trancducers I simulated the beam in Matlab, and positioned them so that the first "side peaks" of interference are just outside the 20 degree spread of the beam.

That gave 70 millimeters apart. Didn't work well enough it seems. But at least one can find big targets if your almost on top of them.

The wreck I shot is about 25 m long, depth 20m, just outside Porvoo, Finland.

Regards,

Henrik

[Rickard]

Hello Henrik!

Your posts are one year old so perhaps you have left the issue of sidescanning. Hope you haven't! I live in Sweden and will visit Porvoo from 22nd to 29th of july to meet with relatives. This presents an opportunity to exchange some experiencies, doesn't it? See my posts on my working system.

Hälsningar (Regards)
Rickard

[Unregistered]

Thanks Richard!

It was nice to see how well your system worked in practice.
Especially I liked the way it could so clearly show the car at 100 m distance!
Unfortunately the photos I took of your screen were quite unusable because of the strong sunlight.
Welcome to Finland another time, hopefully you have a nice towfish to show by then. Good luck!

Best regards,

Henrik

[Unregistered]

can you send me plans, schemas, photos an interface to laptop please.
Thanks for all

[Unregistered]

excuse me, my e-mail is [email protected]

[gaucho1961]

Very Good !

Friend,
Very good its SCAN, congratulations, will have more photos would like much look, also it archetype that you constructed.
Great I hug !

[Clondike Clad]

VERY GOOD

i would like to build one

[Rickard]

Beam patterns of fishfinder arrays.

Hello Henrik

and all who still hope for the solution on the problem of optimizing fishfinder arrays!

I have reported, at length, on my efforts to solve the problem of optimizing Dan Fountain's fishfinder array in my thread "Functional fishfinder array". As a complement to testphotos and simulations I made a practical test of the beam pattern. The test was done in a very simple way. I aimed the array at a floating concrete barrier at an angle of about 30 degrees. The perpendicular distance to the barrier was 28.5 m. The arrangement with an angle made the lobes hit the barrier at different distances depending on their angle from the mainlobe. The lobes were seen at the display as bands at different 'depths' - distances. The instrument (Humminbird Matrix 37) has a Real Time Sonar (RTS) window on the right side of the display that shows the strength of the echo at different distances. The RTS data can indicate the strength of the mainlobe relative to the sidelobes (if sidelobes are visible). Thus, the test setup allowed for measures of angles between sidelobes and mainlobe and the relative strength of lobes. Of course, there was no chance for exact measures, only rought estimates were possible. But I think the results were rather interesting anyway. I tried with one, two, three and four transducers by connecting or disconnecting individual transducers in my array. In general, the patterns confirmed the predictions from the simulations. The visibel part of the mainlobe echo in the last photo with four transducers is about 2.5 degrees wide. I try to attach a zip-file with photos and comments.

Regards
Rickard

PS Sture has done it again.... http://www.subsc305.com/

[Francisco Xavier]

Good practical aproch Rickard.
I have a Matrix 37 too and I have assembled five piezos each side transducer (455 KHz) pointing 30º downward and keeping the the dept 200 KHz transducer facing down for altitude measure. This long ducer is fited on a towfish and towed 12 meters behind the boat, 3-4 meters deep.
The picture I get was not so good resolution but I think I made a mistake not isolating well the backside of the piezos with foam (I used sintetic foam instead of coark - and the epoxy bi-compound react with that foam destroing it)
I have to start again dissolving epoxy with ketone and reassemble the ducer again.

Thanks for sharing

[Rickard]

Thanks Francisco,

I remember your project with the 455 KHz piezos and your method to recover piezos from transducers by putting them in ketone. Perhaps your problem with resolution has to do with the spacings between piezos. I think you used a configuration with unequal spacings. To my experiance these configurations are possible to optimize but the optimal solutions have many sidelobes at about - 5 dB. Unfortunately, it seems as if the instruments displays echoes at least down to this level. The effect of this is several ghost images and 'fish arhes'. The arches are caused by solid objects that reflects sound better than the surroundings. But this is what I have seen in my own experiments. I can't be sure you have the same effects in your tests.

My next experiment will be based on from-the-shelf transducers but I will bring the piezos close together by grinding down the housings. Interpiezo distances below 1/4 of a wavelenght (about 2 mm at 200 KHz) should give sidelobe suppression down to at least -10 dB. This is almost as good as an ideal unshaded linear array with rectangular piezos (this is the principle of Sture Hultquist's arrays). Grinding on transducers might be tricky but Airmar had the guts to say that this wouldn't destroy a transducer. Humminbird will be back with an answer on the same question but I will test-grind on one of their transducers to check the effect anyway. If things work well I will join four grinded transducers in an array. Lenght, and thus angular resolution, won't be impressive but the array can be expected to work well at close range. I will be back with reports from any testings.

As a Matrix 37 owner, have you got the code for entering into 'super user mode' (this is not in the manual)? I can mail the code if you need it. In this mode one can control several parameters that are set automaticly by the instrument in normal mode. This allows for overrunning some settings that assumes you are looking straight down only for finding fishes.

The link to Sture's last 'catch' seems dead now. Try this instead: http://www.alandseawrecks.com


Regards,
Rickard

[Francisco Xavier]

Thank you Rickard,
Below I post 3 pictures what I did. The black transducer is the Huminbird original ducer and the other 8 ones are 455KHz piezos I put before on ketone.
After welding and wiring them in parallel way I glued epoxy using a wooden box to fix temporarily. My mistake was using sintetic foam beteewn two rows of piezos and the epoxy resin react with that foam.

I would be thankful if you e-mail me the code for entering into 'super user mode' and how I can implement it.

Thanks Rickard