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

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.

Scott wrote:
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.

Boy I'm glad for that "IIRC" I put in there. Thanks.

--

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

No problem! The Navy kept fairly quiet about their ELF communications.
They shut down the ELF transmitters a little over a year ago. Wonder
what they're using as a replacement? They were doing experiments with a
satellite based green laser I had heard (while I was still working at
Project ELF)...The ELF signal used MSK modulation (Minimum Shift
Keying), which is similar to RTTY, only the shift between Mark and Space
was 4 or 8 Hz, depending on rate of transmission. Took 5 minutes to
send 3 alpha characters...most hams wouldn't have the patience to copy
at that speed



Scott



Tim Wescott wrote:

Scott wrote:

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.

Boy I'm glad for that "IIRC" I put in there. Thanks.

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

"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