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Acoustic Modem For A Hobby AUV
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Michael
electronics forum Guru Wannabe


Joined: 03 May 2005
Posts: 190

PostPosted: Thu Jul 06, 2006 6:02 pm    Post subject: Acoustic Modem For A Hobby AUV Reply with quote

Hi,

I'm building an AUV for hobby use, however I'm having trouble whe it comes
to communications. So far I've considered sending DTMF tones through 2, 2
way radios, and encoding sets of numbers on R/C equipment but neither will
travel/penetrate far enough (<3m).

It needs to be a duplex system capable of transmitting 32 on/off comands and
8 values (0-255) through about 100m of water.

So far I've found lots acoutic modems except they are more for industrial
use and so are rather high-spec compared to what I need.

So, can you guys suggest where to start (happy to learn any new skills I
have to) or if you can think of a better method I'm open to ideas,

Regards,

Michael
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pbdelete@spamnuke.ludd.lu
electronics forum Guru Wannabe


Joined: 15 Sep 2005
Posts: 273

PostPosted: Thu Jul 06, 2006 6:08 pm    Post subject: Re: Acoustic Modem For A Hobby AUV Reply with quote

Quote:
I'm building an AUV for hobby use, however I'm having trouble whe it comes
to communications. So far I've considered sending DTMF tones through 2, 2
way radios, and encoding sets of numbers on R/C equipment but neither will
travel/penetrate far enough (<3m).

It needs to be a duplex system capable of transmitting 32 on/off comands and
8 values (0-255) through about 100m of water.

So far I've found lots acoutic modems except they are more for industrial
use and so are rather high-spec compared to what I need.

You proberbly know that atomic subs use very low frequency less than 3 kHz
asfair to send to a submarine. Maybe slightly higher frequencies would be ok
in this case.

As for acoustic, maybe you could either try to use a modem + waterproofed
speaker/mic. If that won't work you might have to implement your own algorithm.
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Michael
electronics forum Guru Wannabe


Joined: 03 May 2005
Posts: 190

PostPosted: Thu Jul 06, 2006 6:36 pm    Post subject: Re: Acoustic Modem For A Hobby AUV Reply with quote

<pbdelete@spamnuke.ludd.luthdelete.se.invalid> wrote in message
news:44ad51aa$0$486$cc7c7865@news.luth.se...
Quote:
I'm building an AUV for hobby use, however I'm having trouble whe it
comes
to communications. So far I've considered sending DTMF tones through 2, 2
way radios, and encoding sets of numbers on R/C equipment but neither will
travel/penetrate far enough (<3m).

It needs to be a duplex system capable of transmitting 32 on/off comands
and
8 values (0-255) through about 100m of water.

So far I've found lots acoutic modems except they are more for industrial
use and so are rather high-spec compared to what I need.

You proberbly know that atomic subs use very low frequency less than 3 kHz
asfair to send to a submarine. Maybe slightly higher frequencies would be
ok
in this case.

As for acoustic, maybe you could either try to use a modem + waterproofed
speaker/mic. If that won't work you might have to implement your own
algorithm.


And I guess I'd then have to apply some form of filter to get rid of echoes
etc?

Michael
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pbdelete@spamnuke.ludd.lu
electronics forum Guru Wannabe


Joined: 15 Sep 2005
Posts: 273

PostPosted: Thu Jul 06, 2006 8:00 pm    Post subject: Re: Acoustic Modem For A Hobby AUV Reply with quote

Quote:
As for acoustic, maybe you could either try to use a modem + waterproofed
speaker/mic. If that won't work you might have to implement your own
algorithm.


And I guess I'd then have to apply some form of filter to get rid of echoes
etc?

Either use the acoustic "media" as half duplex. Ie wait until sent waves have
faded out. Or use the "usual" echo cancelation techniques.
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Luhan
electronics forum Guru


Joined: 10 Dec 2005
Posts: 365

PostPosted: Thu Jul 06, 2006 8:08 pm    Post subject: Re: Acoustic Modem For A Hobby AUV Reply with quote

Michael wrote:
Quote:
Hi,

I'm building an AUV for hobby use, however I'm having trouble whe it comes
to communications. So far I've considered sending DTMF tones through 2, 2
way radios, and encoding sets of numbers on R/C equipment but neither will
travel/penetrate far enough (<3m).

It needs to be a duplex system capable of transmitting 32 on/off comands and
8 values (0-255) through about 100m of water.

So far I've found lots acoutic modems except they are more for industrial
use and so are rather high-spec compared to what I need.

So, can you guys suggest where to start (happy to learn any new skills I
have to) or if you can think of a better method I'm open to ideas,

I did an audio system that worked in excess of 4000 feet. You could
adapt it for data quite well.

Get a matched pair of 40Khz underwater transducers.

Send baseband async ascii in narrow band fm at 40Khz.

Decode with standard PLL fm detector at the reciever.

Turn off transmitter when done to allow communication in the reverse
direction.

Data blocks you send should have some kind of error detection
(checksum). Since you are running both directions, you can do
re-transmissions in case of error.

Luhan
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joseph2k
electronics forum Guru Wannabe


Joined: 30 Jun 2006
Posts: 108

PostPosted: Mon Jul 10, 2006 12:22 am    Post subject: Re: Acoustic Modem For A Hobby AUV Reply with quote

Michael wrote:

Quote:
Hi,

I'm building an AUV for hobby use, however I'm having trouble whe it comes
to communications. So far I've considered sending DTMF tones through 2, 2
way radios, and encoding sets of numbers on R/C equipment but neither will
travel/penetrate far enough (<3m).

It needs to be a duplex system capable of transmitting 32 on/off comands
and
8 values (0-255) through about 100m of water.

So far I've found lots acoutic modems except they are more for industrial
use and so are rather high-spec compared to what I need.

So, can you guys suggest where to start (happy to learn any new skills I
have to) or if you can think of a better method I'm open to ideas,

Regards,

Michael

I do not remember where i picked this one up but; if you use an carrier in
the 25 to 35 kHz range and directly AM or FM the carrier and then use about
2 foot (600 mm) dipole antennas you get about 500 to 1000 yards (m)
transmission ranges (at 10 W). IIRC there were some experiments done
somewhere around Florida in the 1970's

--
JosephKK
Gegen dummheit kampfen die Gotter Selbst, vergebens.  
--Schiller
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