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Old July 30th 05, 05:17 AM
Roy Lewallen
 
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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