[TowerTalk] A different dipole design

[Jim Brown]

On 12/22/2024 7:05 AM, Stan Stockton wrote:
> If you just draw this on paper it looks like a dipole that is 20 feet shorter than a normal dipole and near the ends you have what looks like an arrow.

Hi Stan,

There are lots of ways to accomplish what you're doing. What K0SN has 
described is one of them that W6GJB, W6JTI, and I have used for county 
expeditions. N6BT (the very good Force 12 designer) has built some 
interesting versions that were all aluminum.

As you noted, there's minimal effect on the pattern or field strength, 
since radiation is done in proportion to current in each segment of the 
wire (nearer the feedpoint), and is minimal close to the ends, where it 
falls to near zero.

As to the coax -- I suggest you model ground as carefully as possible. 
Feedpoint Z of dipoles varies sort of like an oscillation around a value 
depending on the timing reflection from the earth and its strength. (I 
learned about this from graphs of feedpoint Z in the ON4UN book.) My 
dipoles at around 120 ft over rocky soil measure in the range of 88 
ohms. An 80 dipole we rigged at 40 ft on a county expedition, also rocky 
soil, came in at almost exactly 75 ohms. In all cases, EZNEC came very 
close to the measured values. My high dipoles are all fed with a very 
good RG11.

> I’ll be glad to send an EZNEC file to anyone who wants to get a better picture of the design.  Just send me an email.

Please do.

73, Jim K9YC