Range and frequency.

[Sture Hultqvist]

Bob


I have tested different frequencys from 40KHz


to 620KHz and I belive the best all-around


frequency is 200-250 KHz.


40K. I did get a range of 2500 meters but


no resolution at all. However I could penetrate


20 meters of the seafloor mud.


100K, range of 400 meters but wooden


wreck is hard to see.


200K I got a range of 200 meters, good signal


level and ok resolution.


500K good resolution and 100 m range.


620K 80m range with a transducer only 100mm long.


Design example for 250K:


Aperture of 400x6mm.


The wawelenght will be 6 mm.


Horisontal beamwidh 6/400 radians = 0.9 degrees.


Vertical beamwidh 6/6 radians = 60 degrees.


It is difficult to do exact calculations since the


exact frequency is unknown until the transducer is ready.


It seems that the free crystals behave slight


different to the one put into the transducer.


I let it be what it will be and tune the electronics


to fit the transducer.


As example my 200K crystals become 220K when the


transducer was tested.


Sture

[bob]

Re: Range and frequency.

Sture,


This information is really great! Thanks!


When you have a beamwidth of 60 degrees, how do you determine the angle of the transducer on the fish? Do you just mount it horizontally, or angle it down somewhat?


Also, with regards to the steel beam you mentioned earlier, what would the width of the beam be? should it be the same as the transducer width, or if it doesn't matter, can it be wider to provide more structural stability??


Finally, I was wondering about obtaining crystals to test with. Do you know of a supplier that is resonably priced? Also, have you used different materials? Is there one material that is clearly best for this application, or are there trade offs between materials?


-Bob

[Tod]

Re: Range and frequency.

Bob,


I got a quote for piezo ceramic plates 1.4" x .35" x .13" thick. 25 minimun for $4.06 each. 2 week lead time. I plan to mount 12 end to end to give me a .4 deg horizontal and maybe 50 deg vertical @500 frequency.


Tod

[Patrick]

Re: Range and frequency.

Tod,


When you order these, can you supply the list with part number, contact info, etc.?


Thanks,


Patrick

[Tod]

Re: Range and frequency.

Piezo Kinetics Inc.


P.O. Box 756


Mill Rd.


Bellefonte Pa.16823


Harry Shirey, Sales manager


814-355-1593 x204


P.N. SP1.4-0.130-0.325-402


Let me know if any one els wants to order so we can put the order in at the same time. That might help Harry.


Tod

[Patrick]

Re: Range and frequency.

Tod,


When do you plan on ordering them?


Patrick

[Sture Hultqvist]

Re: Range and frequency.

The downtilting angle of a sidescan transducer


is normally 20 degrees but it is not critical.


"Steel beam" ? I not sure about the question.


I guess it is about the steel backing on the backside


of the crystals and this have nothing to do with


any angle.


Price for crystals is little tricky since I found


it complicated to buy small amount of crystals.


Price in larger batches is however less than


10 USD /pcs.


Sture

[Tod]

Re: Range and frequency.

Maybe Friday. I'm going to get 25 for my self,that takes care of the min. how many do you want and does any one else want some?


Tod

[bob]

Re: Range and frequency.

I would be interested.


Do they come in different thicknesses? That is one issue that I am still unclear about.


Perhaps Sture can help with this!! He sent me a n email at one point, saying that his elements were 3x4x50mm. He has explained how the length and width affects things, but I am not sure about depth..


I am going to make a separate post about materials. Perhaps we can share ideas on other things as well.


-Bob

[Patrick]

Re: Range and frequency.

Tod,


I am interested. However, I might suggest that you wait a few days until everyone is in agreement that they are the best choice.


Could you hold off until next week on the order?


Patrick

[Tod]

Re: Range and frequency.

No problem, I'll wait.