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From: Donald.Heller@jpl.nasa.gov (Don Heller)
Subject: Re: Help: fish finding technology
Message-ID: <Donald.Heller.221.0009AB0E@jpl.nasa.gov>
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Date: Mon, 26 Sep 1994 17:40:01 GMT
Xref: glinda.oz.cs.cmu.edu sci.electronics:102201 comp.robotics:13849

In article <3653ad$e2d@sol.ccs.deakin.edu.au> elmo@Deakin.Edu.Au (Andrew Elms) writes:

>How does those fish finders that everyone seems to have on their
>boats nowadays work. Is it simply ultrasonic pings? I would
>really like to build one. |-)

>Elmo

I used to build these in the early '60s.  The new technology with LCD
screens and plotters may be what you want.  The early devices used a
200 kHz Barium titanate crystal about 2 inches diameter, a half inch
thick.  We pulsed a short burst of 200 kHz and listened for a response.
In strictly depth meters, we just charged a capacitor until the return,
driving a meter.  For fish finders, we used a zenon flash tube which
rotated around the circumference of a depth scale, which flashed
heavily on the bottom return, and flashed lightly on anything which
intervened, either large fish or schools of fish.  The principal in
the modern devices is similar, just better readouts and memory for
bulding a moving map.

Don Heller (Donald.W.Heller@jpl.nasa.gov)
           (heller@vraptor.jpl.nasa.gov)
           (73632.454@compuserve.com)

LASCIATE OGNE SPERANZA, VOI CH'INTRATE

