[TowerTalk] Rising Input Z with more radials?

[Tom Rauch]

> If the radiation resistance is 26 ohms and I measure 38
ohms feed impedance
> at resonance, then apparently I have 12 ohms of ground
loss, for an
> efficiency of:
>
> 26/(26+12) or 26/38 = 68%
>
> At least, that's where I'm at for the moment. Time for
another 8 radials.

While you can watch for a change and that is good,
regretfully we cannot calculate or estimate efficiency of
most real-world antennas using that method even though it
appears in books. There are far too many things that
influence feedpoint impedance. The only way I know of to
estimate efficiency based on impedance is to measure
impedance in the open operating environment, and then to
close off space with a conductive enclosure some distance
from the antenna. This permits and then prevents coupling or
radiation to space. In that case the resistance with
radiation and the resistance with radiation prevented can be
used as above. A removable copper sphere covering your
neighborhood might not be practical or welcome.

What I have found here from field strength measurements is
FS can still increase even when I could not detect a
reduction or change in feedpoint resistance.

What I have done is install a small stable reference antenna
some distance away and watched the field strength there as I
added wire. It does not have to be far away, maybe a
wavelength or less is still OK.

73 Tom