Brian,
after replying to your posting I began to think you had elevated radials and
not a grounded connection. So you have the antenna designed so that it is
resonant and the feedline shield is connected at a point of low impedance, I
assume? I ran a NEC-2 sim with a 1/4 wavelength horizontal radial (to represent
the worst case feedline length) to see how much shield current there is. It
takes only a couple hundred ohms of balun Z to reduce the shield current so
that it is 10 dB below the antenna current. That's a fair number of ferrite
beads up in the air. Or, is the feedline routed straight downward with the
shield acting as the antenna conductor? And are you running RG174 or some other
small coax? A very interesting antenna.
I have wondered if a half wave balloon vertical is the way to go. Fed against
earth ground with or without radials. I have run 1/2 wavelength verticals on 20
meters with great results. What type of balloon are you using? I am interested
in trying a similar setup for the CQ 'test.
Dave WX7G
From: Brian Moran<mailto:brianmo@yahoo.com>
To: DAVID CUTHBERT<mailto:DAVIDNNAN@MSN.COM> ;
topband@contesting.com<mailto:topband@contesting.com>
Sent: Monday, December 13, 2004 10:44 PM
Subject: Re: Topband: elevated vertical matching
I left a bunch of "extra" feet on the vertical
radiator, four elevated radials (choke-isolated from
ground), 200K of static bleed resistance. I pulled
wire down until the MFJ-259B read about 1.2:1. Maybe
I'll try 3/4 wave this weekend :-).
--- DAVID CUTHBERT <DAVIDNNAN@MSN.COM<mailto:DAVIDNNAN@MSN.COM>> wrote:
> Steve,
>
> The radiation resistance of your balloon vertical
> will be 36 ohms. By the time you add in ground
> losses you will be up to around 50 ohms. I would
> just feed it at the base and tweak the length to
> resonate it at 1830 kHz (or whatever you like). This
> antenna will cover over 100 kHz with a VSWR below
> 2:1. I would just put it up, base feed it, and fine
> tune it with a good tuner at the shack. As long as
> the VSWR is below 6:1 at resonance things should be
> fine.
>
> Dave WX7G
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>
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