Topband: Traditional or off-center fed 160m vertical design?

[Clive GM3POI]

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 at contesting.com] On Behalf Of Robert Fanfant
Sent: 06 November 2016 19:17
To: topband at 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



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