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RF under sea water? Sending data through water with acoustics — Parallax Forums

RF under sea water? Sending data through water with acoustics

ArchiverArchiver Posts: 46,084
edited 2001-09-28 04:00 in General Discussion
I'm afraid RF cannot propagate in sea water at any practcal distance. Sound
waves or ultrasonics could be used but you will need special transducers
(Hydrophones) that I believe are quite expensive. For low rate data
transmission it is possible that low priced transducers for fishing sonar
applications could be used.

However, I do not know where to obtain these, Hope this might help a
little. Suggest you try with Edmud Scientific in USA.

Regards.
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>Thread-Topic: [noparse][[/noparse]basicstamps] Sending data through water with acoustics
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>To: <basicstamps@yahoogroups.com>
>From: "Nathan Brown" <nbrown@t...>
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>Date: Wed, 26 Sep 2001 22:28:04 -0700
>Reply-To: basicstamps@yahoogroups.com
>Subject: RE: [noparse][[/noparse]basicstamps] Sending data through water with acoustics
>
>There are a couple manufacturers of underwater communications gear.
>They all use radio waves modulated to a certain frequency. I know
>Uwatec is one, but there are a couple others. That might be one way to
>go.
>
>Nathan
>
>
>
Original Message
>From: Bill Sherwood [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=qBOZrMMsv5F0jyCVolHVJkV7Tu0vGvAv09SqV0jp3VjsK9E_74joURbNohRcbeLCZSvlQT3PTuZ3-gphUy9iwR4]bill.sherwood@p...[/url
>Sent: Wednesday, September 26, 2001 9:27 PM
>To: basicstamps@yahoogroups.com
>Subject: [noparse][[/noparse]basicstamps] Sending data through water with acoustics
>
>
>Hi,
>
>Rather than deal with all the problems associated with running a cable
>to
>the surface from an instrument at 100m seawater depth, I'm interested in
>
>sending some data using acoustics. Baud rate could be around 300 as I
>am
>only sending short strings of data every ten minutes or so.
>
>Can anyone suggest methods or possible ways I could attempt this, or if
>it
>is feasible? What frequency or transducer is best?
>
>Cheers,
>Bill
>
>
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Comments

  • ArchiverArchiver Posts: 46,084
    edited 2001-09-27 17:04
    Mouser has sealed 40 khz transducers that work short
    distances (a few feet) fine. Have'nt tried DX, but who
    knows? The price is right, a few bucks. Might be worth
    a look.

    Jack

    Jose Luis Juarez wrote:
    >
    > I'm afraid RF cannot propagate in sea water at any practcal distance. Sound
    > waves or ultrasonics could be used but you will need special transducers
    > (Hydrophones) that I believe are quite expensive. For low rate data
    > transmission it is possible that low priced transducers for fishing sonar
    > applications could be used.
    >
    > However, I do not know where to obtain these, Hope this might help a
    > little. Suggest you try with Edmud Scientific in USA.
  • ArchiverArchiver Posts: 46,084
    edited 2001-09-27 18:39
    Electrostatic transducers used for air applications will not work
    underwater (Polaroid, Mouser etc). It will be immediatly damaged if
    submerged.
    Underwater acoustics require specially designed piezoelectric xducers.
    Matching rx and tx frequency power/sensivity and propagation path is
    very critical for distance comms.
    ACJacques


    goflo@p... wrote:
    >
    > Mouser has sealed 40 khz transducers that work short
    > distances (a few feet) fine. Have'nt tried DX, but who
    > knows? The price is right, a few bucks. Might be worth
    > a look.
    >
    > Jack
    >
    > Jose Luis Juarez wrote:
    > >
    > > I'm afraid RF cannot propagate in sea water at any practcal distance. Sound
    > > waves or ultrasonics could be used but you will need special transducers
    > > (Hydrophones) that I believe are quite expensive. For low rate data
    > > transmission it is possible that low priced transducers for fishing sonar
    > > applications could be used.
    > >
    > > However, I do not know where to obtain these, Hope this might help a
    > > little. Suggest you try with Edmud Scientific in USA.
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    > from the same email address that you subscribed. Text in the Subject and Body
    of the message will be ignored.
    >
    >
    > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
  • ArchiverArchiver Posts: 46,084
    edited 2001-09-27 23:45
    Hi A.C. -

    The transducers were not immersed, just the faces were in contact
    with liquid. Worked OK, no apparent smoke.

    The sensors (Mouser 255-400ER18 (RX) and 255-400ET18 (TX) do not
    have the usual mesh screen - The face is polished aluminum..

    regards, Jack

    A.C.Jacques wrote:
    >
    > Electrostatic transducers used for air applications will not work
    > underwater (Polaroid, Mouser etc). It will be immediatly damaged if
    > submerged.
    > Underwater acoustics require specially designed piezoelectric xducers.
    > Matching rx and tx frequency power/sensivity and propagation path is
    > very critical for distance comms.
    > ACJacques
    >
    > goflo@p... wrote:
    > >
    > > Mouser has sealed 40 khz transducers that work short
    > > distances (a few feet) fine. Have'nt tried DX, but who
    > > knows? The price is right, a few bucks. Might be worth
    > > a look.
  • ArchiverArchiver Posts: 46,084
    edited 2001-09-28 00:24
    May not smoke, but will not work. I already have tried and they cant't
    release enough power.
    Regards
    ACJacques

    goflo@p... wrote:
    >
    > Hi A.C. -
    >
    > The transducers were not immersed, just the faces were in contact
    > with liquid. Worked OK, no apparent smoke.
    >
    > The sensors (Mouser 255-400ER18 (RX) and 255-400ET18 (TX) do not
    > have the usual mesh screen - The face is polished aluminum..
    >
    > regards, Jack
    >
    > A.C.Jacques wrote:
    > >
    > > Electrostatic transducers used for air applications will not work
    > > underwater (Polaroid, Mouser etc). It will be immediatly damaged if
    > > submerged.
    > > Underwater acoustics require specially designed piezoelectric xducers.
    > > Matching rx and tx frequency power/sensivity and propagation path is
    > > very critical for distance comms.
    > > ACJacques
    > >
    > > goflo@p... wrote:
    > > >
    > > > Mouser has sealed 40 khz transducers that work short
    > > > distances (a few feet) fine. Have'nt tried DX, but who
    > > > knows? The price is right, a few bucks. Might be worth
    > > > a look.
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    > from the same email address that you subscribed. Text in the Subject and Body
    of the message will be ignored.
    >
    >
    > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
  • ArchiverArchiver Posts: 46,084
    edited 2001-09-28 00:51
    Good Day:

    You might want to try: http://www.airmar.com/

    They are probably the largest supplier of marine
    sounder and speedo transducers worldwide.

    I was thinking you could hack a cheap marine depth
    sounder for your purpose. Most of what you need would
    already be constructed and they are available all
    over.

    Regards,

    Andy

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  • ArchiverArchiver Posts: 46,084
    edited 2001-09-28 04:00
    When in doubt, mention Tesla :-)

    As I recall, there's an entire section in one of the Tesla books
    (the big red book with all of his notes in it) about underwater
    RF in salt and fresh water. I'd just go look it up right now,
    but it's buried under rocks and garbage at the bottom of a
    closet.

    Something about 4.3 mhz... don't remember what. Any Tesla fans
    remember this?

    -Chilton
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