Mike, KH6ND, and I installed a SteppIR BiggIR 6-40m vertical
in just such a fashion on Palmyra Atoll, KH5. There is a roughly 40 x 150
ft. warehouse/shed about 25 feet high at the peak being used as a
maintenance facility. It has a steel sheetmetal roof. I mounted a supporting
pipe to the one of the A truss roof supports then through the roof about 60
feet in from one end. The antenna sits a foot above it. I ran a short #10
jumper from the ground lug on the antenna housing to a point under the roof
cap where I attached it to the skin. The antenna is guyed (as recommended)
as it should always be.
The antenna performed well. With the ability to tune the antenna by
adjusting its radiator length I got roughly 1.5:1 VSWR on any frequency band
I wanted (within the design range, of course). The antenna is also being
used on marine HF bands.
We also installed a second antenna on top of a 73 foot tower with only
radials for 40m (3 each). This is a compromise to minimize the visual
impact. They parallel the Phillystran guys to the same guy points.
The warehouse antenna is mounted within 100 feet of the lagoon (towards the
South). The tower antenna is within 50 feet of the lagoon. In the northerly
direction the tower antenna outperformed the warehouse antenna by typically
one S unit. To the South (and the salt water) they both performed about
equally. To the North they must traverse the island (roughly 100 yards of up
to 70 foot trees).
Both of these antennas were kindly funded and donated by the NCDXF. They
were redirected after performing well on the K7C Kure Dxpedition.
73, Aloha
Kimo Chun, KH7U
> From: Robert Bogash <rbogash@centurytel.net>
> Date: 2006/08/16 Wed PM 05:20:30 CDT
> To: towertalk@contesting.com
> Subject: [TowerTalk] Elevated Vertical with No Radials on Metal Roof
>
> I have an interesting QTH, and am mulling over a new elevated HF
> vertical. I have studied all the usual suspects on eHam etc and poured
> over the Champion report on vertical antenna performance.
> Unfortunately, it is now a little dated and Steve, K7LXC says no
> follow-on work has been done. And, I have corresponded with a few of
> the manufacturers.
>
> My QTH can be seen here: http://www.rbogash.com/ham.html
>
> I have a large expanse of saltwater extending 180 degrees in front of my
> house, pointing at all the good places, which would make a vertical
> really shine. And, I have a large 24 gage steel roof, which I think
> would make a great ground plane, and, er, obviate the need for a tuned
> radial system.
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