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.

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.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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

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

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

I hope this will format better (viewed with fixed width font):

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

Roy Lewallen wrote:
. . .
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

Slight correction...our (U.S.) subs using ELF worked at about 50-80 Hz.
I worked at one of the land-based transmitters for 5 years.

Scott


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.

"Roy Lewallen" bravely wrote to "All" (17 Dec 05 12:44:06)
--- on the heady topic of " Underwater"

RL From: Roy Lewallen
RL Xref: core-easynews rec.radio.amateur.antenna:221425

RL The attenuation of a radio signal through water is staggeringly high
RL except at extremely low frequencies. Fresh water is lossy for two
RL reasons: one is that the polar molecules attempt to align themselves
RL with the oscillating electric field. This physical motion results in
RL loss.
[,,,]

Thanks for the info. I had read that submarines communicated in a
band of a few 10's of Hz because of the problems with water. As for
the polar molecules aligning themselves, this implies it takes some
time to achieve. Thus there is a resonnant point in this and if there
is resonnance then there might be anti-resonnance too. Might you know
where this natural molecular resonnance is? Might this be the standard
microwave oven frequency?

A*s*i*m*o*v

Asimov wrote:

Thanks for the info. I had read that submarines communicated in a
band of a few 10's of Hz because of the problems with water. As for
the polar molecules aligning themselves, this implies it takes some
time to achieve. Thus there is a resonnant point in this and if there
is resonnance then there might be anti-resonnance too. Might you know
where this natural molecular resonnance is? Might this be the standard
microwave oven frequency?

Sorry, I don't know. If any of the readers of this newsgroup do, I'd
really appreciate your enlightening us.

Roy Lewallen, W7EL

On Sun, 18 Dec 2005 07:03:23 GMT, "Asimov"
wrote:

"Roy Lewallen" bravely wrote to "All" (17 Dec 05 12:44:06)
--- on the heady topic of " Underwater"

RL From: Roy Lewallen
RL Xref: core-easynews rec.radio.amateur.antenna:221425

RL The attenuation of a radio signal through water is staggeringly high
RL except at extremely low frequencies. Fresh water is lossy for two
RL reasons: one is that the polar molecules attempt to align themselves
RL with the oscillating electric field. This physical motion results in
RL loss.
[,,,]

Thanks for the info. I had read that submarines communicated in a
band of a few 10's of Hz because of the problems with water.

The BW is a product of the information bit rate and the fundamental
frequency. Water enters the picture to drive the fundamental
frequency.

As for the polar molecules aligning themselves, this implies it takes some
time to achieve.

Displacement time by ionic polarization can be as short as s/10¹³

Thus there is a resonnant point in this and if there
is resonnance then there might be anti-resonnance too. Might you know
where this natural molecular resonnance is? Might this be the standard
microwave oven frequency?

For water? salt water? at what temperature? Ice, whose relaxation
time can vary one order of magnitude for each 10°C, is considerably
different from water. Its conductivity plunges like a rock with
temperature too (at roughly the same rate) to become a nearly perfect
dielectric.

The relaxation time for Ice runs in the kilohertz whereas for water it
is in the high gigahertz (and has nothing to do with the microwave
oven frequency as simple heating shifts this relaxation time one order
of magnitude between freezing and boiling). Yes, 6 orders of
magnitude change when going from 0° ice to 0° water.

Attenuation figures may follow this post.

73's
Richard Clark, KB7QHC

As I remember, we used 18 Kc and 13 Kc. We didn't have hertz in those days
:)

We were able to copy Jim Creek when submerged in the Red Sea. Jim Creek had
13 miles of wire suspended between two mountains in what was probably the
worlds biggest capacitance hat.

All CW , because even a 150 cycle shift for rtty would have thrown the tank
circuit out of resonance. Now no one would be able to copy it...


"Roy Lewallen" wrote in message
...
Asimov wrote:

Thanks for the info. I had read that submarines communicated in a
band of a few 10's of Hz because of the problems with water. As for
the polar molecules aligning themselves, this implies it takes some
time to achieve. Thus there is a resonnant point in this and if there
is resonnance then there might be anti-resonnance too. Might you know
where this natural molecular resonnance is? Might this be the standard
microwave oven frequency?

Sorry, I don't know. If any of the readers of this newsgroup do, I'd
really appreciate your enlightening us.

Roy Lewallen, W7EL