[PSUBS-MAILIST] Sonar/Telephones was Propulsion

["Gary R. Boucher" <protek@shreve.net>]

     I did my dissertation on a scanning sonar system that I built using 
three 8-degree cone transducers.  These are standard frequency for most 
units at 192KHz but the pattern 8 degrees is narrow.  I pan and tilt the 
system giving a 6 by 6 array of what's in front of the sonar's 
location.  The main reason that most fish finders operate on 192KHz is the 
resolution.  As the frequency goes up, the resolution gets more defined 
(i.e. fish).  For longer ranges sonars can use the 30-40 KHz 
frequency.  This frequency does not have as much resolution to pick up 
small fish but travels further in water with less attenuation of the signal.
     I built my own "Ping" generator from a transformer I wound and two 
TIP-120 darlington pair transistors.  I also built the receiver using 
several analog filters and wide-band op-amps.  The whole system worked far 
better than I had hoped even though I used wire-wrap fabrication for 
analog, usually a no no for analog of that frequency.  I first took it to 
the LSU-Shreveport pool where I was allowed to be the only show in the 
water for a couple of hours.  On the first ping my receiver was totally 
flooded with returned echo.  I lowered the gain and tried again.  I finally 
had to set the amplifier's gain at the almost minimum setting to be able to 
track a swimmer (one of my student assistants).
     In field trials it worked very well the second time.  The first time I 
hit the sonar head on an object and knocked it out of alignment as I had 
not tightened the alignment nuts.  Anyway, I built a small 8-foot wooden 
boat for the trials and attached a bracket to hold the sonar below the 
waterline.  The boat was attached to a fishing boat alongside and towed.  I 
have never attached the sonar to my sub although I built it to fasten below 
the bow with no trouble.
     I am sure that my dissertation is in some of the archives if anyone is 
interested in my circuits or methods.  I do not have it in electronic form 
with photos and schematics all bundled together.  Basically, if you have 
some electronic expertise you can build a really neat sonar with standard 
parts you can buy.  If you want a telephone I would suggest using a 
broad-pattern transducer and modulate it.  I know some are single side 
band, some are FM.  I would assume you could use AM modulation with less range.

Gary Boucher


>Oh, by the way, I've been experimenting with ultrasonic transducers and 
>modems. I hooked one up in a fish tank (no fish in it :) )  I had to rig 
>up (build) a mini pulser on the transmission end and a discriminator 
>circuit on the receiving end to eliminate the noise, reflection, etc., but 
>I was able to send a  document under water (22 inches) after about 60 hrs 
>of work. Does anyone know the resolution of ultrasonic waves over 
>significant distances (500 ft.)? Also does anyone know the the best 
>frequency for the most limited degradation of signal?