KJ4FDV: "Sounds great if the ground resistance stays the same for a
given ground system with different antenna lengths. But that is an
assumption." ....
KJ4FDV: "I will lengthen my inverted L to 3/8 wl and measure the
feedpoint resistance, subtracting the modeled 52 ohm radiation
resistance to get ground resistance. " ....
That may get you a ground resistance as seen from the feedpoint, but it
won't get you the ground loss because, as you noted, the current maximum
moves further out the radials. Approximating the ground loss as a
resistor at the feedpoint seems to work fairly well for short antennas
but not for antennas over 1/4 wavelength. It does work OK for
calculating the feedpoint impedance but not for calculating power loss.
Remember you can't get the radiation resistance (or the gain or the
impedance) of an inverted L using a Mininec ground because there will be
a low horizontal wire above this ground which will contribute error.
To compound those problems, many people with a lot of modeling
experience believe that NEC (both NEC2 and NEC4) underestimates near
field ground loss for very low wires.
Jerry, K4SAV
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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