[TowerTalk] Change in Frequency with Height above Ground

[Jim Brown]

On Thu,5/26/2016 8:24 PM, Don W7WLL wrote:
> Lowering the height of an antenna above ground, such as a beam, will cause the resonant freq to decrease, increase?

Decrease. But not always -- I have a 10M beam at about 15 ft that goes 
up! The variable here is mutual coupling between elements and between 
elements and ground.

Another error in using SWR as the indicator of resonance is that 
feedpoint Z changes with height, and in a very complicated way (and 
because of mutual coupling to ground). In general, low dipoles (as a 
fraction of a wavelength) are lower Z, high dipoles are higher. AND -- 
feedpoint Z is also affected by the quality of the ground.

SO -- we may THINK the resonance is affected by the height as indicated 
by the low value for SWR, but it's actually the feedpoint Z changing!

73, Jim K9YC