submersible 20kHz+ speakers (underwater comm)

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I'm wondering if anyone has a source for submersible speakers that are in the 20kHz+ range. Also useful would be mics that could hear them! I'm thinking about underwater communication. Do you think RF would still be better? I'm afraid that RF wouldnt communicate far enough where as sound travels very well through water.

Does anyone have any general input on this topic?

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Sonar transducers? Fish finder variety?

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How far are you talking about? What speeds are you after too?

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There are commercial underwater comm systems used by divers. I suspect that they are ultrasound (maybe 40-50KHz) AM or FM modulated with communications bandwidth (300Hz to 3KHz or so) audio.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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Some 50m would be nice I think. Speeds - say 115200 baud. Thinking about building a remote controlled submarine, but want to know what I'm getting into.

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I guess you mean 50m from you, how deep do you want to go? I'm guessing you only mean a few metres down? I would think that VHF or even low band UHF radio would still work ok. Maybe look at some 433MHz transmitters.

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Try Airmar at
http://www.airmartechnology.com/

Depth sounder or fish finder xducer should do the job. One transducer will do Tx and Rx. Lower frequencies go further but for 50m the 200KHz transducer will be fine.

Most efficient use of power is usually ssb but you probably won't need to worry about comms power consumption compared to other consumers.

Don't get too fancy with high baudrates, multiple reflections will cause lots of problems, you may need to look into channel identification, echo cancellation etc - maybe a standard modem will be a good start.

Klave
GK

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I agree about baud rates and channel quality. Ultrasound under water can be a real challenge. Especially if the vehicle is close to the bottom or some strong reflecting surface (like a ship hull).

And, for safety, build some strategy into it that does the "right thing" if signal is lost!

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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Excellent. Thank you, that was exactly the kind of information I was hoping to get.

Cheers!

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If you find some transducer you must build a modem that translate the data into modulated acoustic signals like FSK or PSK, preferably including error correcting codes and synchronizing signals. The signal must be amplified to a relatively high voltage since the ceramic transducers have a high impedance, and at the receiving end it gets even worse than this!

At short ranges and narrow depths it is probably better to use some cable/rope, it can be designed to float on the water surface too.