Tim Wescott wrote:

Asimov wrote:

Hi,

I was thinking about why radio wave communications are not generally
used underwater. Basically I'm asking what are the quantitative
components of the underwater medium that makes it impractical except
for perhaps very short ranges. Things like attenuation, impedance,
etc... Does any one here know these details or have them handy?

A*s*i*m*o*v

... Acme Corp: Unlimited credit for disadvantaged coyotes.

The conductivity of water causes great attenuation at all but very low
frequencies. Think "skin effect".

That having been said, the US Navy (and probably all other folks with
subs) use extremely low frequency RF (30kHz IIRC) to communicate with
strategic nuclear subs.



Penetration of water by radio waves is directly proportional to
wavelength. The longer the wave length the further the penetration of
water. That's why the Navy uses extremely long wave length signals to
contact deep submergence subs. Even then it takes a very long time to
transmit a very short three or four letter message. Of course the sub
then has to raise up to just below the surface and extend an antenna
mast to contact the COMNAVSAT for its full message.

Dave WD9BDZ