Topband: Vertical question
George (K8GG) & Marijke Guerin
gmguerin at voyager.net
Fri Sep 5 11:36:23 EDT 2008
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
At the risk of repeating some information in the archives, I offer the
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,
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