[TowerTalk] Choke on feed point of dipole

[Jim Brown]

On 1/13/2026 1:53 PM, David Gilbert wrote:
> Default ground specs were used.  (0.005/13 over Real/MININEC)

Ground quality both close to our antenna and in the far field have a 
profound effect on vertically polarized antennas. There's useful 
information in my study of the heights of vertical antennas, and how 
they, and the signals they radiate, interact with the surface of the 
earth, for soils that differ greatly from one QTH to another.

Verticals care as LOT about ground quality and a bit about height. The 
electromagnetic nature of the soil varies a LOT from one QTH to another. 
In granite mountains where I live, ground is lousy for RF. 30 miles to 
the east is Silicon Valley, wildly developed, so lousy ground. 50-7 
miles to the east is fertile soil with pretty good electromagnetic 
properties, another 30 miles east and it's wine country, not great soil 
for radio. That's where N6RO is, and they were never the biggest signal 
on the lower bands when I lived in Chicago, even though they had a great 
antenna farm.

Horizontal antennas care NOTHING about soil quality but EVERYTHING about 
height.

I live in the Santa Cruz mountains, which is mostly granite with a layer 
of "duff" -- a rather absorptive soil comoposed of centuries of the 
small bits of vegetation that fall off the redwoods throughont the year, 
but especially during storms. As we walk through it, our feed are 
cushioned by the softness of it. Well into our rainy season, when that 
duff gets increasingly saturated, the only useful vertical in my antenna 
farm,  a Tee for 160M, works better. On higher bands, the absorption 
from the trees and the lousy soil makes verticals useless, while high 
dipoles for 80 and 40 work great. The highest dipole I could rig for 
160M was at 120 ft, not quite a quarterwave. The optimum height of a 
horzontal antenna for those lower bands is 1/2 wave.

  A horizontally polarized antenna at a quarter wave is as low antenna, 
with poor field strengthen at low to mid-high angles. For more than two 
years after I moved here, I had a 160M dipole at 120 ft and a 100 ft Tee 
with a lot of on-ground radials, some pretty long, some shortened by the 
location of buildings and other concrete. I did a LOT of on-the-air 
comparisons with the two, and the dipole rarely won (but it did with 
certain propagation conditions, as any on-air student of propagation who 
could have switched between multiple antennas would have experienced.

I strongly suggest that you look at my work on this, and that you follow 
my suggestions in an earlier post about plotting the vertical patterns 
of the two antennas on the same axes. There, and using the cursor to put 
dB numbers to the differences, we see that the antenna whose current 
maxima has significantly greater field strength at lower angles, which, 
on average, makes for greater DX performance. Yes, a few dB. But any 
serious contester in a limited station will tell you that 2 dB, and 
sometimes 1 dB, can be the difference between a QSO or not; or longer to 
make it with QSB.

Being sure of ourselves is not a great way to learn stuff we missed the 
first time around.

73, Jim K9YC