Acoustic will get you plenty of range, but it may be difficult to
understand.  The problem with acoustic is that any body of water becomes
a "hall of mirrors" and your command gets through but so do many echoes.
 With shallow bodies of water there are thermal and other focusing
effects such that the echo may be stronger than the original signal.
Also the echo structure may change on the time scale of the waves on the
surface so ondinary telephone echo cancellation doesn't work.
        On the other hand my company does this all the time, that is why we get
the big $$$ ;-)  It is an interesting challenge, and for low data rates
such as controlling a submarine it may work.  A good source of theory
info are books by Robert J Urick.  If you have infinite money you can
buy gear from Benthos who just bought Datasonics(www.benthos.com).  The
traditional frequency range for this is 10-14kHz, but anything up to
100kHz will work for 100 meters or so.  Fishfinder transducers are
cheap, but directional.

Douglas Butler (aka Sherpa Doug)
Senior Engineer
Imetrix Inc.
1235 Route 28A
P.O. Box 152
Cataumet, MA 02534-0152
tel. (508) 564-6460
Fax (508) 564-6860
dbutler@imetrix.com

> -----Original Message-----
> From: Heinz Czychun [mailto:hczychun@BLVL.IGS.NET]
> Sent: Monday, July 09, 2001 6:34 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]: Underwater RF
>
>
> Hi John,
>         Something I've been thinking about. Instead of rf why
> not acoustic.
>
>         I'm sure someone has tried something like this ?
>
>         Would pulses sent on say a 40khz carrier update the subs
> controls frequently enough ? I'm sure you would get better range than
> rf. There would probably be interference problems to overcome with
> multiple transmitters (fish finders ?). And how much range is really
> necessary before the sub goes out of sight.
>
>         I finally found what looks like a reasonable supplier of
> acoustic transducers.
>
>         http://www.hexamite.com/he123tr.htm
>
>         Does anyone know of other similar suppliers.
>
>         I havn't ordered from them as I haven't yet had time to try
> some experiments.
>
> At 2:35 PM -0700 7/9/01, O'Reilly John E NORC wrote:
> >Has anyone ever tried transmitting from above water to
> underwater and vice
> >versa?  I am thinking of using 2m amateur transceivers on
> either end, and
> >I'm wondering what kind of range I can get with a couple of
> watts.  Also, if
> >I put one half of the antenna (either ground or radiator) in
> the water, will
> >that make a difference?
> >
> >TIA
> >John
> >
> >--
> >http://www.piclist.com#nomail Going offline? Don't AutoReply us!
> >email listserv@mitvma.mit.edu with SET PICList DIGEST in the body
>
> --
> http://www.piclist.com#nomail Going offline? Don't AutoReply us!
> email listserv@mitvma.mit.edu with SET PICList DIGEST in the body
>
>
>

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu