A metal roof is indeed a wonderful groundplane for a vertical antenna. In
the early 1980's I installed a 35' marine whip antenna and an automatic
tuner on the top of an aircraft hanger in Sacramento, CA. The transceiver
was a Sunair GSB-900DX ... 100 watts out from 1.6 - 30 MHz.
This system replaced an aircraft HF transceiver (most likely a 400 W
Collins) with the aircraft coupler and a random wire.
The Collins installation had severe range problems in most areas, and
actually couldn't be used for close-in (less than 100 miles) work.
The antenna was centered on the roof peak, and was well bonded to the
roof support steel structure (welded some 6" pipe with a matching flange
for the antenna and a plate for the coupler). The feedline was 150-200
feet RG-213 run down the roof and into the existing cableway used by the
old system.
Sadly, the RF amplifier fried on the first power up test ... we were only
getting 2-3 watts indicated on a Bird 43 ... but that was enough to
activate the tuner. With this combination at this low power, we
consistantly outperformed the Collins installation. In fact, we had loud
and clear comms on all frequencies from 2 MHz through 22 MHz (the unit
didn't have any assigned frequencies above 22 MHz).
We then replaced the PA with the spare and demonstrated full power ops.
The operators loved it and immediately shut down the Collins equipment
(removing it later that week).
If you don't have a 100 x 200 roof to use ... guess you'll have to make
do, but a 30 x 30 roof will really work well. If you feel you need longer
radials, simply connect them at the eaves and continue them to the ground
and away from the building.
Make sure your roofing material is well connected together electrically.
The hanger I worked on had steel everything, and had what appeared to be
stainless steel screws holding the aluminum roofing onto the steel. Lots
of screws.
73,
Rick, WB3EXR
On Fri, 14 Aug 1998 05:54:22 -0600 Rod Greene <w7zrc@micron.net> writes:
>
>Dave, I have often wondered how a vertical would play if
>mounted on top of a metal roof. Could the metal roof
>panels be used for the 'ground' instead of radials? It
>would seem that the roof would actually be better than
>radials. Any ideas? I have a metal roof over my shack ..
>
>Rod
>
>At 10:02 PM 8/13/1998 -0500, Dave Nissen wrote:
>>Hello to all..
>>
>>I need your help with my new vertical anntenna..
>
>>Now to the problem.. I plan on installing the anntenna on a 30'X30'
>roof of
>a metal building.. Does anyone have a idea as to how to make/install
>the
>radials?? The anntenna will be mounted on a tri-pod, the roof is about
>15'
>high, from ground level..
>>
>
>>TNX
>>73
>>Dave de W9COP
>
>
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>
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