VE4XT replied to W7DDD:
>Remember, the whole idea of radials, particularly in ground-mounted
>applications, is to emulate as closely as possible a continuous sheet of
>metal, which your roof is.
Except that we're above ground here, where the radials need
to be resonant. I once had far more roof to work against
(maybe ten times the area) & was not really impressed with
how it played.
By play I mean how it worked.
Where does the roof begin to look like a big sheet of metal,
instead of an odd length of wire? Model an elevated vertical
fed against a few radials of incorrect length & see what it
looks like, especially when the radials are too long.
A 30m monopole fed against radials for 80m looks more
like a high angle antenna. I have not been able to compare
against another antenna enough to get a feel if this is really
what is going on, but sure has me rethinking my elevated
verticals.
The best success I've had with a metal roof like that is
with radials (laboriously trimmed) suspended a bit above it
(roof roughly 1/4-wave square on 80m, with an HF2V in the
center).
If I had no choice, this is a job for a SteppIR - though would
gladly swap any metal roof for a place on Twin Spits Road
any day. ;^)
73, VR2BrettGraham
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