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Richard wrote:
"I have access to a 65 ft. water well that I could install a radial in." A radio wave traveling along the surface of the earth has its electric lines of force tilted slightly forward so that the direction of propagation is slightly tilted downward. The earth is a poor conductor as compared with copper. The earth absorbs and dissipates some of the wave`s energy. Skin effect is the phenomenon of high-frequency current concentration on a conductor`s surface. Skin effect applies to earth as it applies to copper, but the penetration depth depends on wavelength and resistivity of the conductor. At 1 MHz, r-f penetrates copper to an effective depth of only 0.0026 in.. The effective skin thiclkness (penetration depth) in the earth depends on its dielectric constant. In ordinary soil the dielectric constant may be 15 and may vary with moisture in the soil. Water has a dielectric constant of about 80. Very dry soil may have a dielectric constant of only 2 to 5. Soil conductivity varies from 1 mmho to 40 mmhos. At I MHz, the effective skin thickness of the earth, with good soil conductivity of 36 mmhos per meter, is about 8.5 feet. At a soil conductivity of 6 mmhos per meter it is 20 feet. For a poor conductivity of 1 mmho per meter the skin thickness of the earth is about 50 feet at 1 MHz. Sea water has a dielectric constant of 80, and has an effective skin thickness at 1 MHz of 0.738 feet. Skin effect thickness varies inversely with the square root of frequency. Point is that contact with the soil at a 65-foot well depth is not important at h-f, as r-f current flow at h-f is mostly confined to the surface of the earth. Skin effect will confine the r-f path from the water surface at the bottom of the well to the surface of the well bore back out of the well to the surface of the earth around the well, if the r-f can be caused to go down the well at all. Highly conductive radials at the surface are the key to an effective ground for h-f unless you are lucky enough to be in close contact with water in the sea.. Best regards, Richard Harrison, KB5WZI |
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