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Underwater communication

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2005-2006 » Archive through 10 November, 2006 » Underwater communication « Previous Next »

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Mike_b
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Username: Mike_b

Post Number: 292
Registered: 05-2005

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Posted on Wednesday, 01 November, 2006 - 12:31 pm:   Edit Post Delete Post Print Post

I have been playing around with mics dropped into the sea, lakes, ponds. Some very interesting stuff going on and surprisingly noisy.

Has anyone got thoughts on how to use water as a short range transmission medium - for say person to person SCUBA communication?

I know VLF is used by the subs.

rgds

mb
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John_becker
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Post Number: 752
Registered: 05-2005

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Posted on Wednesday, 01 November, 2006 - 12:39 pm:   Edit Post Delete Post Print Post

Mike, as a scuba diver, we just used signs, but I believe it can be done, judging by recent footage on BBC TV. But I think the full-face masks they used allows a mic & speaker to go inside to pick up voice. Probably short range radio link between communicants, but as to what type I dont know.

J
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Externet
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Post Number: 79
Registered: 05-2005


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Posted on Thursday, 02 November, 2006 - 04:05 am:   Edit Post Delete Post Print Post

Hi.
I worked in the middle seventies with the inventor of the scuba communicator. (Mr. Ernesto Alcívar, a navy officer, my electronics mentor and diving buddy.)
He received the U.S. patent because of the innovation of implementing VOX and noise filters.

Of course the mask has to be full face, the noise filter is to avoid the bubbles and breathing from activating the VOX, and the use of two microphones. One to pick the speech inside the mask and another worn attached to the throat, as contact microphone or transducer to activate the VOX.
The system carrier was modulated ultrasonics, simplex operation. Radio does not work.
The hardest stage of the development was the hermeticity of the container for the circuitry, and finding waterproof connectors.
The microphones were encapsulated in vulcanized rubber to avoid exposure and corrosion.

Miguel
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Mike_b
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Post Number: 293
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Posted on Thursday, 02 November, 2006 - 06:15 am:   Edit Post Delete Post Print Post

Miguel - very helpful, thanks.
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Davy
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Username: Davy

Post Number: 19
Registered: 06-2005

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Posted on Friday, 03 November, 2006 - 11:25 am:   Edit Post Delete Post Print Post

I am a hobbyist in radio controlled model submarines which we control down to about 3m deep using standard transmitters at 40Mhz.

I also designed (and sell) a Pinger system. This is an emergency beacon to help locate them if lost! It works with underwater sound at audio frequencies with a range of about 20m in a quiet pond. It doesn't transmit data other than "Help I'm still here"!

David
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Mike_b
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Post Number: 294
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Posted on Friday, 03 November, 2006 - 05:41 pm:   Edit Post Delete Post Print Post

Thanks Davy,

Again, very helpful information. I note you dont use VLF ... yet.

I am now wondering if I can just connect a transducer driven at audio frequencies to the water - it will need some very clever filtering - I feel that my old digital filtering books will get a dust off.

rgds

mb
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Davy
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Post Number: 20
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Posted on Monday, 06 November, 2006 - 08:33 am:   Edit Post Delete Post Print Post

Audio will work over short ranges but with a lot of distortion, I think.

I seem to remember from my diving days that early attempts were audio - waterproof speakers etc. There was even some sort of rubber sphere tht you could speak into!

David
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Davy
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Post Number: 21
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Posted on Monday, 06 November, 2006 - 12:07 pm:   Edit Post Delete Post Print Post

Mike,

Just dredging my memory, I have seen someone controlling a R/C sub whilst diving using a waterproof transmitter (FM,35Mhz)!
The main requirement is to have the aerial insulated from the water(TX and RX) I think.

I tried a 433 MHz module and the range underwater was mm!

Penetration under water is very much a matter of frequency. With VLF you get hundreds of metres, I believe. Mind you the transmitter ceases to be hand held! (Some of the biggest ,longest transmitters on earth.)

I would be very interested to hear more about your digital filtering trials. I have had a MAX275 chip recommended but I never got round to trying it.

Hope this helps your thoughts.

David
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Mike_b
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Post Number: 295
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Posted on Monday, 06 November, 2006 - 12:43 pm:   Edit Post Delete Post Print Post

Wow - it never fails me the diverse information available from this site !!

Thanks Davy - Im not at the design stage yet. I am guessing that, to restore audio, there will quite a bit of filtering, which I would love to avoid if possible.

Im wondering now if a sort of terminal keypad and display might be a better solution. I can then use, say, binary encoding ultrasonic/RF as the carrier coupled to tried and tested error correction and detection software.

rgds

mb

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