Rob,
An off set top loading will radiate unlike a balanced top loading. Far better
to eliminate Horizontal radiation unless you want to be louder within a couple
of hundred miles. Resonate the vertical at say 1.89, then place a hairpin coil
across the feed point to bring the antenna to 1:1 at the wanted operating
frequency. Your proposed antenna will need a good feed point choke. 73 Clive
GM3POI
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Robert
Fanfant
Sent: 06 November 2016 19:17
To: topband@contesting.com
Subject: Topband: Traditional or off-center fed 160m vertical design?
I am planning on putting up a 160m T vertical next week. After doing some
modeling , I would like your thoughts concerning using a traditional ¼
vertical design, versus an off center fed design.
My modeling of the traditional designs approaches 36-38 ohms of real impedance
while the off center fed design shows I can obtain close to 50 ohms of real
impedance.
Details:
Trees on my property are roughly 143’ tall and I can’t use ground mounted
radials for a variety of reasons. I found I can get up to 110’ feet of usable
vertical length, assuming radials @ 20’ off the ground. The antenna will be
suspended between trees.
I’ve discovered through modeling using elevated radials at 20’ , a 110 vertical
section. By varying both the radial and T top section lengths , I can design a
160m vertical which approaches 50 ohms of real impedance , using an off center
fed design. It exhibits excellent characteristics from what the modeling shows.
Based on the modeling I’m leaning towards the off center fed design primarily
because It has a lower SWR at resonance (1.83Mhz) than the traditional
vertical, and removes the need for building/adding a matching network if I
only want to cover the lower portion of the band (CW). Thoughts?
-rob N7QT
Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|