[TowerTalk] Horizontal Dipoles

[Jim Brown]

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