"Jim Lux" wrote in message ...

On 6/2/2011 10:21 AM, Wayne wrote:
I'm looking into mounting a vertical (20 meters and higher freq) on a
new patio cover. The cover is made out of 6 inch by 16 foot aluminum
channels that interlock edge to edge across a 20 foot width. Each
section is powder coated (aka...."painted"), so the sections are most
likely not well connected electrically to each other.

I'll bet they're better connected than you think. Are there sheet metal
screws joining them? what's holding the strips to the frame? Can you put a
wire/foil tape under the screws. In any case, it would be easy to bond the
panels together with some short jumpers. I can think of a variety of ways
to do this, but one of the easiest might be a strip of copper foil tape
along the 20 foot length. Sand the powder coat away on a spot on each
"strip", run a stainless sheet metal screw through the copper foil or braid
and the aluminum. Then glop on something to seal it so it doesn't corrode
or leak. Butyl roof mastic might be a good thing.

Yes, there are various connections with sheet metal strips running across
all the channels, and a self tapping screw into each channel. There are
connections between everything, but a little uncertain as to the quality of
the connections.

A fancier way would be to get another aluminum strip and spot weld it.


I'm considering a 10 foot long H shaped metal structure lying on the
cover, with the antenna mounted in the center of the H. Radials are a
possible but not desired approach. Any other suggested methods of
mounting the antenna/etc.?

You need to seriously think about bonding the roof anyway, so that is your
best bet.

But, capacitively coupling from something lying on the surface would also
probably work fairly well. Wide aluminum flashing laid out from your
antenna base across the top of your corrugations (bend it to fit the
ridges) and glued down might work pretty well.

If you had, say, 1 foot wide by 10 feet long, and it's 1/8" max distance,
that's like a capacitor of about 500pF. Put a couple or three of those
strips and you're doing pretty well. For your frequencies, it's like it's
actually physically connected.
-
Thanks for the comments. I'm still at the stage of wandering around and
planning.



--Wayne W5GIE