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From: dale@lamont.ldgo.columbia.edu (dale chayes)
Newsgroups: sci.electronics
Subject: Re: Data xfer UNDERWATER !
Summary: Too high!
Message-ID: <3530@lamont.ldgo.columbia.edu>
Date: 23 Mar 91 17:45:20 GMT
References: <430.27e07fdb@brb.isnet.inmos.co.uk> <18928@milton.u.washington.edu>
Organization: Lamont-Doherty Geological Observatory N.Y.
Lines: 30

>>> In article <430.27e07fdb@brb.isnet.inmos.co.uk> robw@brb.isnet.inmos.co.uk 
>>asked for suggestions about telemetry (persumably of data) over 10 feet, 
>>perhaps, or sometimes underwater.
>>
>> In article <18928@milton.u.washington.edu>, whit@milton.u.washington.edu 
>(John Whitmore) observed (in my words) that wires were out, and light might 
>pose problems of alignment, so he suggested a tuned dashpot and 110 baud data
>rates, or if in fresh water, how about 49 megs (presumably RF) remote control 
>systems.
>

Its not impossible to get above 110 baud, but its not easy. See the articles 
in the Ocean Engineering issue I mentioned the other day.  Small, high
frequency (on the order of 50 to 300 kiloHertz) transducers are easy to come
by (they are used in fish finders, ultra sound imaging,  and depth sounders 
for small boats.) You don't have to do much to protect the cables/electronics 
in 10' of water.

National makes an  ultrasound transceiver (IC) designed for acoustic 
operation in this range. Its an LM1812, and the specs and application 
discussion are in Volume 3 of the National Linear databook.  Included in 
their "typical applications" are sources for transducers.


(Standard Disclaimer....)
-- 
Dale Chayes Lamont-Doherty Geological Observatory of Columbia University
Route 9W, Palisades, N.Y.  10964	dale@lamont.ldgo.columbia.edu
voice:	(914) 359-2900 extension 434	fax: (914) 359-6817