Underwater Data Link?

Hi Eric

First thought is that I have read somewhere about underwater antennas. They were a lot shorter than what you have in air and the attenuation was much worse. Might be worth some research. If you (say) ran a couple of hundred kilohertz you could FSK or PSK that at some low data rate. Perhaps even drive it with one of the older 1200/75/300 modem chips. (ie RS232 serial data) I mean this is how the US subs get their action messages (although this is a really low data rate)

Next one is a laser diode connection to some modem. I note that in the cell phone world one can connect a laser/optical fibre device direct to the RF output stage of the TX. This may sound far fetched but I wonder about using a laser diode and phototransistor connected to an ethernet switch. I have NOT thought this through at all so pls done burn me too hard!

I think the data rate of using an acoustic path would be way too low. You have to allow for major multipath reflections through the medium and I see this as bringing it down dramatically. There are probably some signal recovery techniques that can be used in this situation but I dont know of them. Personally I'd like to fiddle with Wyman/RDFT encoding in a voice bandwidth and see if that works. It has adjustable forward error correction which might just make it do-able. You tend to need a PC at each end though!

Apologies for the waffling

Cheers Bob Vk2YQA

Eric wrote:

Hi,

Don't want to get side-threaded, but I got hit up on a project idea that should prove practical, educational, fun, and just plain neat.

What will be required, however, is a wireless data pipe down to a depth of ~50 feet (15m). Unfortunetly, it will have to be wireless.

(Obviously, such a link will also have to be acoustic and not RF.)

I can't go outside of "consumer" price tags though. By "consumer", I'm thinking up to ~$500.

Depth time on a full battery charge of at least 30 mins is prefered.

Standard data ports, such as ethernet or RS-232.

I'm not concerned about the data rate through the water, or what mechanism/schemes these modems use going through the water (proprietary, I'd imagine), as long as the data ports use standard communications.

If the modems behave and function (from their physical ports, not modem-modem through the water) as a standard "analog modem", I plan on using just a terminal program with the surface modem. Port speed should be a non-issue, as long as its standard. Even just 300 bps will work fine.

If the modems behave and function (port side, again) as standard "network cards", then I'll be doing TCP/IP. Again, only need the bare minimum data rate for function.

It would be nice if such modem could function like both above, giving more flexibility, but I can do with either.

Its not going to be passing graphics, images, or anything extensive through the water. In fact, the relevant data it will be passing will only be 15 to

20 characters in length.

I "thought" that I had seen such an (consumer) animal in the past years ago, and mentally noting that it "neat", but I may be mistaken. My googles are only turning up such modems that are either commercial or military, obviously outside my reach.

Just throwing this out in hopes that maybe someone has seen such an animal with a consumer price tag -- or possibily an idea or two on how to maybe creatively homebrew such hardware, relatively inexpensively, out of existing hardware. If need be, I can kludge up power supplies and waterproof casings (able to withstand 15m) for anything creative...

Thanks!

Cheers Eric

Also this

Looks like a system at 150Mhz.

Maybe use a 2M txcvr, a shortened antenna and a packet TNC! Lots of these can be bought second hand very cheaply.

I assume you are licensed to use amateur equipment?

Eric wrote:

At one Computex (Taipei) I attended, there was a company showing an Ethernet hub that worked under water. This was a wired network.

Bob, I suspect if he wants to go wireless, he is going to have to go further down the RF Spectrum than a couple of hundred khz, even for that short a distance. The OTS comm systems for their full face masks have a range just slightly over what he desires, operate around 30 khz SSB. At that frequency, he is not going to be able to move a great deal of data very fast but as I recall, that was not a factor. I use an Aladin AirZ hoseless computer and I think the transmitter operates around that same frequency range.

Nice to see folks from "VK" land here with us.

73 OM Andy WD4KDN

Its all intriguing anyway! Not that I have a large enough body of water nearby to try experimenting with it though.

I did a quick bit of browsing around and even found some experiments done by a VK5 using 160M

I note he has some attenuation curves that might be worth a look at. Although some kind of packet, PSK or other kind of digital system would work in an SSB bandwidth the problem for the OP is that he probably doesnt want to take a PC with him underwater! Still think a packet TNC at 300BPS might be usable though.

I am actually here in more ways than one.. Am living in East Texas.

Cheers Bob W5/VK2YQA

nitespark wrote:

Probably more than $500 but worth a look

Dennis

I agree Bob. Quite interesting. I was diving last weekend in a quarry with two other divers who had wireless comm systems using full face masks. I could hear them talking to each other but couldn't make out what they were saying. They have been trying to talk me into purchasing a full face mask with comm but at present, I have other financial priorities. I guess for a very limited distance, 160 meters might work but depending on the application, battery size and the associated tx power would be limiting factors. The article mentioned floating an antenna to the surface. If you were to do that, you might as well use VHF or UHF depending on distances and power outputs, etc. For most divers, I would think that would not be their first choice because of entanglement issues.

If you are in East Texas, depending on where, you are getting pounded by "Rita". Hope all goes well. Perhaps we can hook up on 20meter?

73 Andy

Yeah I know. Some news broadcast had someone on that had been evacuated from 4 different shelters.

Sort of like it was here with Isabelle last year (or year before). She ripped up the coast of NC and VA. 20-25 miles east of here there were downed trees and it got worse the further east you went. Around here it got a little breezy and that was about it. The barometric pressure dropped substantially at my house.

I had plans to dive Va. Beach that weekend, but it had torn up some much stuff and they were evacuating people, no since in going down there. Lost the money I had on my hotel reservations but there were LOTS of people in Virginia Beach who lost a LOT more than that.

Thus spake nitespark :

I have family in Tyler. It was a "non event" there, according to my bro. Further east it turned to shit. Imagine being evacuated from NO to Houston to Texarkana. Talk about being shit upon.

Hi,

(This is reply to both of your messages, along with a reply to others in this thread as well.)

Apologies for not getting back to this thread until now. I had something come up that kept me busy all weekend, and it looks like it will continue to do so until early next week. :/

I did read all the replies though and all were very helpful. That link you gave for the PDF will be very helpful as well. I've only had time to briefly skim over it, but look forward to reading it in detail as I'm not familiar with propagation through water at all.

The laser idea is pretty cool. (Wonder if IR would work at all, have to look that up later.) From googling, found some other folks that put together some homebrew robotic projects and had various levels of success using DTMF. They were using generators/decoders just for simple commands, but got an idea in my head brewing on how to turn sequences into characters (with even some rudimentary CRC), and not requiring any computer coding at all.

As for a license, unfornutely I don't have one (yet). I do have experience with commercial and military communications though (mainly SHF, tactical and fixed SATCOM, LOS/Troposcatter microwave, etc) on both the radio side (converters, synths, amps, filters, antennas, ect) and data side (muxes, modems, ect). Planning, when time avails, to go to a local ham radio meeting and getting involved with the hobby.

Cheers!

-Eric

Where would you find 20 meters to hook together?

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