Michael wrote:
This has been done since the beginning of radio. Nothing new. However, I am
interested in the sand antenna. I would love to hear more about working
antennas that exist entirely below ground. I am guessing but would say this
would not work on any band above 160 meters. I know the Navy has made huge
underground radiators at frequencies like 50 khz. I would be surprised to
hear that something as high as 1.8 mhz could be made to work.

I recall reading some years ago about underground antenna experiments
done by the military. I believe the were done well into the HF range. A
trench was dug, the antenna put into the trench but not in direct
contact with the soil, then the top was covered. The objective was to
make a concealed antenna for relatively short range communication. The
signals were much weaker than for an above-ground antenna (~30 dB if I
recall correctly, but I might not), but still usable for the purpose at
hand. This shouldn't be surprising.

Roy Lewallen, W7EL

You might be interested in the 1918 article on underground antennas.
http://www.rexresearch.com/rogers/1rogers.htm

"Roy Lewallen" wrote in message
...
Michael wrote:
This has been done since the beginning of radio. Nothing new. However, I
am
interested in the sand antenna. I would love to hear more about working
antennas that exist entirely below ground. I am guessing but would say
this
would not work on any band above 160 meters. I know the Navy has made
huge
underground radiators at frequencies like 50 khz. I would be surprised
to
hear that something as high as 1.8 mhz could be made to work.

I recall reading some years ago about underground antenna experiments
done by the military. I believe the were done well into the HF range. A
trench was dug, the antenna put into the trench but not in direct
contact with the soil, then the top was covered. The objective was to
make a concealed antenna for relatively short range communication. The
signals were much weaker than for an above-ground antenna (~30 dB if I
recall correctly, but I might not), but still usable for the purpose at
hand. This shouldn't be surprising.

Roy Lewallen, W7EL

Fred W4JLE wrote:
You might be interested in the 1918 article on underground antennas.
http://www.rexresearch.com/rogers/1rogers.htm

Thanks for the reference. A key observation from it is:

"One of the Naval experts present mentioned that it had been found that
the penetration of the ground wave component increases with an increase
in wavelength. This is an important fact and helps to explain the
operation of this new radio system, with its aerials buried in the ground."

I believe this method is still being used for communications to
submarines. It depends heavily on the very great skin depth and
relatively low attenuation in sea water at the VLF wavelengths used.

The buried antennas I was referring to operate, as far as I know, with
normal field propagation through the air, not through the ground.

Here are the skin depth in feet and attenuation per foot in salt water:

Freq Skin Depth Atten
ft dB per ft

10 MHz 0.23 37
1 MHz 0.73 12
100 kHz 2.3 3.7
10 kHz 7.4 1.2
1 kHz 23 0.37
100 Hz 74 0.12

And here they are for average ground:

Freq Skin Depth Atten
ft dB per ft

10 MHz 13 0.66
1 MHz 25 0.34
100 kHz 74 0.12
10 kHz 230 0.037
1 kHz 738 0.012
100 Hz 2300 0.0037

So communication through the ground or even salt water is practical at
low frequencies. High frequency is another matter, though. But that
doesn't preclude using buried antennas for sky wave propagation.

Roy Lewallen, W7EL

Back in the day, we received traffic from the station in Jim Creek while
submerged. They used a 13 mile array strung between 2 mountains. IIRC it was
on 18KC. CW only as any frequency shift would have put the finals out of
resonance. Much better methods today that remain classified.

I know we could receive it when submerged in the Red Sea.

"Roy Lewallen" wrote in message
...
I believe this method is still being used for communications to
submarines. It depends heavily on the very great skin depth and
relatively low attenuation in sea water at the VLF wavelengths used.

The buried antennas I was referring to operate, as far as I know, with
normal field propagation through the air, not through the ground.

So communication through the ground or even salt water is practical at
low frequencies. High frequency is another matter, though. But that
doesn't preclude using buried antennas for sky wave propagation.

Roy Lewallen, W7EL

"Fred W4JLE" wrote in message
...
Back in the day, we received traffic from the station in Jim Creek while
submerged. They used a 13 mile array strung between 2 mountains. IIRC it
was
on 18KC. CW only as any frequency shift would have put the finals out of
resonance. Much better methods today that remain classified.

I know we could receive it when submerged in the Red Sea.

"Roy Lewallen" wrote in message
...
I believe this method is still being used for communications to
submarines. It depends heavily on the very great skin depth and
relatively low attenuation in sea water at the VLF wavelengths used.

The buried antennas I was referring to operate, as far as I know, with
normal field propagation through the air, not through the ground.

So communication through the ground or even salt water is practical at
low frequencies. High frequency is another matter, though. But that
doesn't preclude using buried antennas for sky wave propagation.

Roy Lewallen, W7EL





Did the Navy ever deploy the Long-Range Autonomous Homing Bottle?

--
Ed
WB6WSN
El Cajon, CA USA

Roy. as you know, radio propagation through the ground follows exactly
the same laws as propagation through anything else.

All is governed by the resistivity, permeability and permittivity of
the medium, at a partcular frequency, and the geometry of the
interfaces between different mediums.

The problem of finding solutions to paricular problems lies only in
entering input data into a general purpose, number crunching computer
program, which I'm sure versions of it already exist.

Reg Edwards wrote:
Roy. as you know, radio propagation through the ground follows exactly
the same laws as propagation through anything else.

Sure. The only real differences among salt water, dirt, and air are the
loss -- which is a big difference -- and propagation velocity.

All is governed by the resistivity, permeability and permittivity of
the medium, at a partcular frequency, and the geometry of the
interfaces between different mediums.

The problem of finding solutions to paricular problems lies only in
entering input data into a general purpose, number crunching computer
program, which I'm sure versions of it already exist.

NEC-4 can handle antennas and propagation in two media of infinite
extent separated by an infinite plane boundary. Neither one has to be
air. While this doesn't imitate some real situations very well, it can
produce some good insights into propagation and the performance of
antennas embedded in a medium other than air.

Roy Lewallen, W7EL