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From: biocca@bevb.bev.lbl.gov (Alan Biocca)
Newsgroups: rec.boats,sci.electronics
Subject: Re: Eagle Fish I.D. and Fish I.D. Plus sonars problems
Message-ID: <6957@dog.ee.lbl.gov>
Date: 14 Sep 90 18:47:33 GMT
References: <2693@s3.ireq.hydro.qc.ca: <656@ghp.UUCP> <151118@felix.UUCP>
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Reply-To: biocca@bevb.bev.lbl.gov (Alan Biocca)
Organization: Lawrence Berkeley Laboratory, Berkeley
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X-Local-Date: Fri, 14 Sep 90 11:47:33 PDT

In article <151118@felix.UUCP: daver@felix.UUCP (Dave Richards) writes:
:In article <656@ghp.UUCP> jim@ghp.UUCP (Jim Stewart) writes:
:>I know they use sound, but at what frequecies?  Some of the transducers
:>talk about different angles of scanning the bottom--is this effectively
:>just an average, or does it do some other function?  How is the
:>transducer made?  Is it some kind of crystal?  Are there two parts to
:>it (i.e., one to generate a sound pulse and one to receive it)?  How
:>difficult would it be to put something together to experiment with the
:>concepts (i.e., build a primitive transducer, or buy just the transducer
:>if somebody knew the pin-out, and hook it to a scope, or whatever just
:>to see how it works)?

:Looking at the specs for the assembled units yields this information: 
:Frequency: 200kHz....  Xducer beam angle: 20 degrees

There are some new models that use 455 khz, and beam angles vary from around
16 to 40 degrees.  I suspect the narrow beamwidths are being accomplished
by building essentially an active dish antenna with/on/attached to the crystal.

:Regarding the other questions: yes, it is some kind of crystal.

My understanding is that it is a quartz crystal.

:To "experiment with the concepts" I think it would be much easier to do it in
:air using a dynamic (coil) speaker as a transducer, a parabolic dish as a
:focussing device, and of course, much lower frequencies, say 1-2kHz. 

I know someone who built some small systems of this type using disk ceramic
capacitors as transducers.  Apparently they (at least some of them) have the
proper electro-mechanical characteristics.  


Alan K Biocca