[Antennas] resonance

[fkamp at comcast.net]

I may not understand all I think I know about resonance.

Take the case of a dipole antenna.

Resonance is where the impedance becomes resistive when the 
length is cut to the desired frequency.  If the dipole is 
flat-topped at 1/4 wavelength above electrical ground, that 
resistive impedance is 75 ohms.

That is what I know.  Is that all there is to it?

What happens when the dipole is not 1/4 wavelength above 
electrical ground.  A chart in the handbook indicates that 
under those conditions the impedance can vary significantly 
from 75 ohms.

My question is does the impedance remain resisitive as the 
height above ground is varied and the impedance changes?

Regards,
Frank Kamp
K5DKZ