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Subject: Re: Echo sounder
X-Newsreader: Forte Agent 1.91/32.564
Date: Tue, 21 Jan 2003 18:51:41 -0800
NNTP-Posting-Date: Tue, 21 Jan 2003 18:51:07 PST
On Mon, 20 Jan 2003 22:55:34 +0100, Jens Rasmussen
>Hi, I just recently bought myself a small (25ft) sail boat. Now, as
>I'd like to think I am a rather experienced electronics designer, I
>thought I'd design some useful gadgets for the boat. First out would
>be an echo sounder to measure depth (not for fishfinding). I have done
>some research, mainly on the net but so far I have only found out
>about how to do the wiring for off the shelf products. I was wondering
>if any of you reading and posting in this group has had any experience
>in designing an echo sounder. What I have managed to find out so far
>Transducer/receiver of piezo material usually putting out 100W-1kW
>short bursts of 30-200kHz sinewaves. The same piezo element is then
>used to receive the reflected pulse burst and the depth is calculated
>by knowing the speed of sound in water (approx. 1500m/s). So far it
>sounds pretty simple but what I'd like to know are things like: What
>impact burst frequency has on performance? Do you really need 100W-1kW
>of burst energy? Do I need to shape the piezo transducer in some way
>(other than circular disc type) to keep the sound beam cone narrow to
>reduce unwanted reflections? How much attenuation do you get from the
>burst travelling in water and reflecting of rock or clay?
>What I was searching for on the net was som d.i.y. story from someone
>building one of these things, but so far I have not found a single
>echo sounder project that isn't using some off the shelf commercial
>product. Could it bee that the complexity of such a project is too big
>to be a d.i.y.?
>Any help on either a real project or some research data on echo
>sounding would be very much appreciated.
This topic could generate a book. To educate yourself on sonar
technology, see if you can locate "Principles of Underwater Sound" by
Robert Urick (ISBN: 0932146627). If you have a technical university
library nearby, they might have this book. This is a good book for
learning about the basics of sonar. The easiest frequency to use is
200 kHz since you can get depth sounder transducers from almost any
boating supply store. Any other frequency will make the cost go up by
a factor of 10 to 100. 200 kHz can easily detect 150 metres depth, in
the Baltic probably more than 200 metres due to the low salinity.
Yes, you do need 100's of watts to drive transducers. Since your
dealing with a low duty cycle, it's pretty easy to build this sort of
power amplifier if you are capable of designing high power pulse
amplifiers and magnetics.
Santa Barbara, CA
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