On 1/10/2022 4:40 PM, Lux, Jim wrote:
The impedance is closer to 50 ohms
Except that feedpoint Z is strongly dependent on soil characteristics
and mounting height, and I've found NEC to be a pretty fair predictor if
soil characteristics are known, at least approximately. My 120 ft high
dipoles for 80 and 40 are >80 ohms, so I feed them with RG11. For a CQP
county expedition to a site where we launched ropes into scrub trees,
max rigging height of 40-50 ft and lousy ground, NEC predicted 75 ohms.
We brought RG11, and an analyzer confirmed it was the right choice.
The variable here, as I understand it, is coupling of the ground
reflection as a parasitic element.
73, Jim K9YC
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