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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