What kind of range would wifi get underwater?

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What kind of range would wifi get underwater?

Postby nleahcim » Mon Jul 05, 2004 5:44 pm

OK I know this is a strange question - but does anyone know what kind of range a 802.11b connection would get in distilled water? I understand it wouldn't be very good range - but anyone have any ideas about exactly how bad it would be? Sorry if this is the wrong section...
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Postby Thorn » Mon Jul 05, 2004 5:54 pm

nleahcim wrote:OK I know this is a strange question - but does anyone know what kind of range a 802.11b connection would get in distilled water? I understand it wouldn't be very good range - but anyone have any ideas about exactly how bad it would be? Sorry if this is the wrong section...

Probably darn close to zero, since water molecules resonate at 2.4GHz. Actually, that's the reason 2.4GHz dies in foliage; all that water in the leaves.

If I recall correctly, RF transmissions in water need long wavelengths, like AM frequencies or lower. I think US Navy submarines use ELF (Extremely Low Frequencies) which use long waves.
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Postby hkelley » Mon Jul 05, 2004 6:21 pm

You would be looking at frequencies of 40-80 Hz to be able to penetrate water and a fair amount of RF power at that to get any distance.
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Postby wrzwaldo » Mon Jul 05, 2004 6:35 pm

nleahcim wrote:OK I know this is a strange question - but does anyone know what kind of range a 802.11b connection would get in distilled water? I understand it wouldn't be very good range - but anyone have any ideas about exactly how bad it would be? Sorry if this is the wrong section...



Bad enough that if your life depended on it you would be screwed. I guess if you wanted to test it you could fill your bathtub with it and drop in the laptop and try to connect to your AP.
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Postby nleahcim » Mon Jul 05, 2004 7:03 pm

[quote="Thorn"]Probably darn close to zero, since water molecules resonate at 2.4GHz. Actually, that's the reason 2.4GHz dies in foliage]
They use VLF (http://www.fas.org/nuke/guide/usa/c3i/vlf.htm) - but that's for longer ranges than I need. I'm hoping to find something that can get me high speed communication through maybe 10-20 feet of water, and 3-30Khz (VLF) isn't going to get me the kind of thoroughput that I need (nor do I have any of the equipment - while 802.11b is common, easy, and cheap)
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Postby Thorn » Mon Jul 05, 2004 7:13 pm

What about a blue/green laser (or LED) if it's only 20 ft max? (Red tends to be absorbed by water.) High data rates, COTS and cheap.
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Postby nleahcim » Mon Jul 05, 2004 7:19 pm

Thorn wrote:What about a blue/green laser (or LED) if it's only 20 ft max? (Red tends to be absorbed by water.) High data rates, COTS and cheap.

How precisely does it have to be aimed? Reason is that it will be moving - so it would be *very* difficult to keep a laser aimed properly at all times. And I googled but couldn't find much of anything. Does the technology have a specific name or anything?
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Postby King_Ice_Flash » Mon Jul 05, 2004 7:19 pm

nleahcim wrote:They use VLF (http://www.fas.org/nuke/guide/usa/c3i/vlf.htm) - but that's for longer ranges than I need. I'm hoping to find something that can get me high speed communication through maybe 10-20 feet of water, and 3-30Khz (VLF) isn't going to get me the kind of thoroughput that I need (nor do I have any of the equipment - while 802.11b is common, easy, and cheap)

I am afraid to ask why you need to use wireless underwater.
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Postby Thorn » Mon Jul 05, 2004 7:36 pm

nleahcim wrote:How precisely does it have to be aimed? Reason is that it will be moving - so it would be *very* difficult to keep a laser aimed properly at all times. And I googled but couldn't find much of anything. Does the technology have a specific name or anything?

Hmmm. Good question. A laser would get diffused in water, but even so it has to be in a rough alignment. There have been article about using light communications before, but I don't think the technology has a particular name. I remember reading that the blue/green doesn't get absorbed by the water like red will.

Uh, what about sonic? Sound travels real well in water. I'd just wonder if it would meet whatever your transmissions speeds need to be.
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Postby I_Died_Once » Mon Jul 05, 2004 9:27 pm

War Diving? :confused:
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Postby Barry » Mon Jul 05, 2004 9:52 pm

Probably underwater robot of some type.
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Postby nleahcim » Mon Jul 05, 2004 11:47 pm

Barry wrote:Probably underwater robot of some type.

Exactly.
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Postby macpad » Tue Jul 06, 2004 1:13 am

I would go with sonic like Thorn suggested, 44KHZ travels very well in water, faster than through the air, plus could easily go to 100ft with cheap stuff, remember thou it's a lot of design, build etc to make you own comms system.
Also if you are in a small tank there are all sorts of echo problems.

You would still be limited by your carrier wave of 44khz, not sure what the max is that you would get out of that (20 ish Kbits maybe, two waves for detect, plus overheads??, I have no idea on that)

Have fun

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Postby King_Ice_Flash » Tue Jul 06, 2004 3:57 am

I would go with a cable. This way when it breaks, you have something to drag it up by.
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Postby Madhadder » Tue Jul 06, 2004 9:17 am

I agree with the above poster.. You can go upto 300ft with Cat5..
Just makesure that the Plugs are well sealed..
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