[TowerTalk] vertical antenna feedpoint

[Jim Brown]

On 3/15/2025 6:19 PM, Tom Hellem wrote:
> You got it. The extra 35 ohms is all loss resistance, heating up the worms.
> Add radials.

There's a lot about radial systems in this slide pdf for talks I've done 
at Pacificon, Visalia, and to several ham clubs, including a lot of ways 
to implement radials or a counterpoise.

http://k9yc.com/160MPacificon.pdf

Once you've got a decent radial system, modeling software like NEC can 
be used to design a simple way to match it to 50 or 75 ohm coax. The 
concept is to increase the length of the antenna to move its resonance 
down in frequency far enough that the resistive component of the 
feedpoint impedance is 50 ohms, which makes it look inductive, which can 
then be tuned out with a suitable capacitor. "Suitable" is this case 
means of a type that has very low equivalent series resistance and a 
sufficiently high voltage rating for the power you want to run. I simply 
added enough length to the horizontal top of my 160M Tee to resonate it 
down in the top portion of the AM broadcast band. I think I ended up 
with capacitance in the range of 800-900 pF.

73, Jim K9YC