RE: [PSUBS-MAILIST] Convention & Hydrophones

[<jonw@psubs.org>]

>From a hydrophone perspective, I think we need some testing to be done by
those who have submersibles.  There's only so much testing one can do on the
surface from a kayak (in my case).  I think we've done a good job of proving
that hydrophones can be made very inexpensively from common parts, and that
they are surprisingly sensitive.  The issue we need to deal with now is
directionality.  Someone told me that a sub acts as a pretty good listening
device all on its own, and that you can hear distant objects quite well.  I
think someone with a divable sub could, with just a few field tests, make a
determination if the omni-headphones we've created add any value for
identifying surface traffic.  Lynn Darnell had a theory in terms of a
"stereo" hydrophone to provide directionality.  JimK suggested using a
housing such as a steel pipe, and somebody else mentioned using a funnel
type object (made of metal) to act as a collector.  To date, only shallow
testing has been performed (50 foot depth or less) and we are likely to see
different results in deeper water of 350 feet just due to the way the sound
waves bounce around.  So there's still alot of experimentation that can be
done in this area.  I'll be putting the hydrophone and pinger slides up on
the website soon so people can build them for themselves.  I also have a
number of hydrophones available that I can ship to people who want to test
them.

In regards to the acoustic pinger, Andy is correct that ABS has specs for
them and the homebuilt 3.2khz buzzer piezo doesn't meet those standards.  If
I remember correctly the ABS standards call for a 37 khz (maybe 37.5 khz)
transmitter and that it be active throughout the entire dive for tracking
purposes.  Since it is ultrasonic, it doesn't bother the pilot.  I know the
Desert Star homing beacon operates at 72.5 khz based upon the SPORT
documentation.  Anyone remember Lee's last name, from the convention.  He is
an electronics guru and showed interest in the ABS specification for the
pinger and suggested he could probably come up with a schematic to build
one.  The homebuilt pinger is inexpensive and easy to build, so from that
perspective it might be able to find use as a supplemental device, but a
device that meets ABS standards should take priority.

Andy, from Desert Star, stayed with us the entire weekend and participated
in all our events.  It was great having him there both as a DSS rep and as a
friend.  Put a lobster and some steamers in front of him and he'll talk all
night about underwater acoustics.  :)

Jon




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