The attenuation of a radio signal through water is staggeringly high
except at extremely low frequencies. Fresh water is lossy for two
reasons: one is that the polar molecules attempt to align themselves
with the oscillating electric field. This physical motion results in
loss. The other is that "fresh" water generally has dissolved salts
which increase its conductivity. Salt water's loss is dominated simply
by its conductivity.

Here are a few numbers for attenuation per meter. It's hard to find good
data on loss in real fresh water, but I did locate a representative
number for one frequency.

F MHz Fresh water Salt water
0.01 3.9 dB
0.1 12
1 39
10 121
100 ~ 50 dB 369

Roy Lewallen, W7EL

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

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