Ed_G wrote:
There is one
problem with this setup, though.... I do not think there is a suitable
ground on the building roof.

I was thinking you could lay some radials on the roof
to obtain your ground plane. You could also insulate
the pole from the mounts using sections of PVC pipe.

I think it would be easier to extend the length of our inverted V
legs. I had posted their length between 35 and 40 feet, but if we run
out of building to extend the ends to, I suppose we could go on
straight down from the end mounts, toward the ground a bit.

I had assumed that your "no compromise" statement included
antenna length. A full-sized dipole would certainly solve
your 75m problem but then the full-wave dipole would be
mostly non-functional on 40m when fed with coax.

Here's another idea. *Change the pole support to fiberglass*,
use heavy duty 300 ohm balanced line, and run the 300 ohm
feedline inside the fiberglass pole to the dipole. You could
use the G5RV length of 51 feet per dipole element. With such
a configuration, the feedpoint impedance on 3.8 MHz would be
about 20-j130 ohms and on 7.2 MHz would be about 100-j450 ohms
which the SGC would have no trouble matching. This could
multiply your system efficiency by maybe 6-8.
--
73, Cecil http://www.w5dxp.com