Peter Schrader, VK4TGV wrote:
Subject: Topband: Vertical question
> Hello all,
> Forgive me if this sounds like a silly suggestion, I have been a long
> time lurker on this list. I am slowly building up my Topband capability
> which is somewhat of a challenge on a 400 square metre suburban housing
> block in the suburbs.
>
> I have put up a vertical, about 18 metre long, with plenty of radials
> and am feeding it with 450 ohm window ladder line, at the house wall
> there is a current balun, and from there about 2 metres of RG213 to a
> MFJ949 tuner.
>
> Has anybody on this list had experience with using open wire type
> feeders with verticals? All of the literature on verticals refer almost
> exclusively to coax feeds.
>
> The main issue I have is limited room, in that a 1/4w 160 m transmitting
> antenna is out of the question, and I want to use it for 80m as well,
> but avoid lossy trap arrangements.
>
> --
> Cheers and 73,
> Peter Schrader
> VK4TGV
At the risk of repeating some information in the archives, I offer the
following:
1. Feed the 18 meter vertical for 80 meters with coax and only use the
tuner to flatten the SWR at the ham shack. Then use the 80 meter vertical
as a support for an inverted-L for 160 meters, so the majority of the signal
is then in the vertical wire instead of in the twin lead Peter describes.
The antenna can be spaced a few feet from the vertical and a short wire at
the base can tie a separate feed point into the ground system. Since RG8
and RG213 are low loss at 160 meters, a 2:1 or 3:1 SWR can be tuned out at
the ham shack with an unbalanced tuner. An L-net tuner has worked best for
the Battle Creek Gang. Alternately, an UnUn can be wound and placed at the
inverted-L feed point to match the inverted-L feed point up to 50 ohms.
2. I, personally, take some exception to not using a trap. Altho'
coaxial traps can be lossy, traps can be made from #10 or #12 copper wire
wound on UV resistant plastic pipe and tuned with door knob ceramic
capacitors. I can give suggested values off line if someone wants to
contact me directly.
GL & 73,
George K8GG
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