Underwater communications

[telemonster]

Greetings from Norfolk, VA.

I've been trying to think up some geek projects that involve underwater communications for an internet television show project I'm involved with.

This is probably more tech than anything, but doesn't seem to fit into the tech categories so I'm posting it to basic questions.

It is my understanding that the hoseless computers (transponder on the 1st stage HP port) use low frequency radio communications. Do they interfere with each other? Can anyone confirm they are RF and not acoustic? I don't recall indepth details in the product brochures (I do not own an air-integreated computer).

One of my ideas was a shore-to-diver data communications setup, fast enough for ASCII text transmission with error correction. On shore would live a GSM/Internet to water gateway device that passes instant messenger traffic from the internet to a diver carried device. (IRC @ 50ft). This will mostly be homebrew. The diver carried device is cake, but the communications link seems to be the hard part.

The target test site would be a quary, in Rawlings Virginia.

Everything I've found in regards to commercial solutions seems to revolve mostly around acoustic transmission of data. Has anyone ever been near a site using an UWA (Under Water Acoustic) data transmission setup? Is it audiable to people?

Anyone know of "radio modems" used for underwater applications? Most ROV's tend to be teathered by an umbilical.

Any thoughts or insight would be appreciated!

 

[CuriousRambler]

The problem with radio waves is that the energy required to change mediums (transmitted in air, recieved underwater for example) is too high to make any practical sense. I'm not sure on this, but I heard radio waves have trouble traveling far in water and lose power fairly quickly.

I think we all know water's an amazing medium for acoustics to travel through, how far off can you hear whales singing?

ROVs are tethered, because nearly every ROV (and probably all of them in a commercial use environment) have sensors like sonar, cameras, attitude, depth, etc, so on top of controls they need to monitor all these feeds at once. Not only is that a lot of data for a transmitter to handle...I'm really not aware of any acoustic transmitters that can carry something like video.

AUVs are probably more in your realm. They're a lot like ROVs in the sense that they're underwater robots, but they have preprogrammed "missions" that they carry out, minor adjustments or commands can be made acoustically.

I think *most* underwater data transfer is done via acoustics, but I'm sure there are more "advanced" things out there. Try waterproofing a cheap R/C car/boat/sub/whatever and see how far you can get the signal to transfer if the transmitter and reciever are both underwater...That might give you some heading to tell you if RF is what you want, and if so the power that may be needed.

 

[telemonster]

We actually have a project (on the burner) that is an AUV... only airborn

The higher the frequency, the more water blocks it. I believe 1/8" of water will kill most cellular signals. Not sure about VLF and HF underwater...

I started digging thru my wiki for notes and found something that I overlooked. I emailed this company that makes this module, I'm sure it's out of my price range... but never know. It is a DSP based aucoustical modem! Seems to have nice range, small form factor:
http://www.dspcomm.com/products.htm

We will see!

 

[CuriousRambler]

I dunno. I've built a few ROVs, and have priced out and drawn up plans for quite a few more (basically the more advanced ones that require more money than I have to make ) and it's pretty surprising how cheap some of those control modules can be. I found quite a few things that I could interface some pretty advanced controls for sub $30, or redundant sonar rangefinder kits for $40. Obviously I ran into a fair number of things that cost WAY more than I could ever hope to afford, but if nothing else, I learned it's always worth emailing and inquiring about a price. More than once I was surprised and thinking "that can't be right.."