Richard Fry wrote:
"Chuck"
It would be more accurate to bill this as "Mediocre radial system vs
20 m x 30 m solid aluminum ground screen ".

I suspect much the same results would obtain for the roof mount, even
if the roof were at ground level.
_____________

When the comparison is made between the roof-mounted version as shown in
my PDF and an earth-mounted vertical using a 2-ohm "broadcast quality"
r-f ground system of 120 buried radials each about 1/4-wave long, then
the advantage of the roof-mount version drops to about 5 dB.


Sounds reasonable. My point was that the
entire 13 dB difference could probably
be explained in terms of the difference
in ground resistance ( 15 ohms vs 2 ohms
vs 1 ohm? for the aluminum roof) and
the extremely low radiation resistance.

N.B. these radiators are electrically very short. Using taller
radiators would reduce the performance difference.

RF

Chuck