[TowerTalk] vertical antenna feedpoint

[Richard (Rick) Karlquist]

What I do on my vertical is:

1  Set the top hat size to resonate the vertical to 1830.
Four sloping 30 foot, 45 degree wires, zip tied to the
four top guy ropes.

2. Use an auto-transformer (AKA an un-un) to increase the
drive impedance from 20 something ohms to 50 ohms.  Note:
an un-un, not a balun.  I make the un-un out of RG58 as
a bifilar or trifilar "winding".

3. If desired, switch in a series capacitor to go higher
in the band, mainly for phone contests.

This tends to give the most bandwidth and efficiency.
Works for me.

73
Rick N6RK

On 3/15/2025 8:23 PM, Jim Brown wrote:

> 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
> 
> 
> 
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