[600MRG] Ground Moisture Effects

[Marshall Cross]

Frank, I looked-up LF/MF conductivity range for Pittsburg taken from Arcone and Delaney, "Electrical Ground Impedance Measurements in the United States Between 200 and 415 kHz," FAA-RD-73-103, AD A 068088. The expected conductivity for your area is between 0.011 and 0.0056 S/m. 73, Marshall, W1HK, #41.

-----Original Message-----
From: 600MRG [mailto:600mrg-bounces at w7ekb.com] On Behalf Of Frank Lotito
Sent: Tuesday, July 26, 2016 3:27 PM
To: 600 / 630 Meter Group
Subject: [600MRG] Ground Moisture Effects

An esoteric question or two about the effects of ground moisture on the tuning of "short w.r.t. wavelength" transmitting antennas, such as the short top-loaded verticals, or small perimeter low-to-the-ground tuned loops.


As the surface ground moisture content, and depth of moisture penetration change with the seasons, in general:


(A) What changes in a more pronounced manner, the (1) ground conductivity, or (2) the ground dielectric constant (relative permittivity)?


(B) Which has the greatest effect on antenna tuning, (1) ground conductivity or (2) ground dielectric constant?


(C) What is the effect of an "increase in ground moisture content" on (1) the antenna's resonant frequency, e.g. increase or decrease the resonant frequency? (2) increase or decrease the antenna's total apparent resistance at the new resonant frequency (sum total of the ohmic loss, skin resistance loss, radiation resistance, etc.?)  (3) Increase or decrease the ground return loss for verticals? (Logic tells me as moisture content increases the ground return losses should get lower.) In order not to cloud the topic, assume that no liquid, snow or ice collect on the antenna wire, tower, mast, its insulators, or tuning boxes.


(D) In general, is the performance of a low-to-the-ground small perimeter transmitting loop more susceptible to ground moisture changes than a short ground mounted vertical?


During my almost 2 years as WH2XHA, at 630 meters I have seen changes in my antenna tuning as the seasons change, and during a particular season as local rain / snow storms temporarily peaked the ground's surface water content and depth of moisture penetration.   (I use a helter-skelter top loaded vertical for 630 meters.) I never attempted to measure the ground moisture content, yet alone measure its effect on antenna tuning.  I do have EZNEC 6.0 (the commercial edition).  Using EZNEC I have tinkered with the ground characteristic and get slightly different resonant frequency results as I change the ground characteristics. However, I am not sure that the EZNEC results represent what I have experienced in the real world.


You assistance in helping me understand the effects of ground moisture on antenna tuning will be appreciated -


73 Frank Lotito K3DZ / WH2XHA






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