> >But the best solution is to have multiple antennas
available to cover all
> TOA
> > conditions.
>
>
> I have asked about this topic a couple times before....But
for those of us
> whose horizon is blocked by surrounding mountains up to 15
to 20 degrees
> elevation angle, is it even worth the effort to put up a
vertical??
Steve,
The biggest problem I see is people consider TOA as some
sort of figure of merit. TOA is totally meaningless by
itself. What needs to be compared (as Bill correctly did) is
the absolute gain at various levels.
There is also a "rub" using amateur type programs to
calculate TOA at low angles on low frequencies. The modeling
programs look at FS a very large distance out from the
antenna over a flat homogeneous earth. You will notice they
show virtually no FS along the ground, even though we very
clearly hear BC stations (and unfortunately power line
noise) for many miles. On 160, the distance the pattern is
shown at actually compares to the height of the ionosphere
above the earth! This may give us the false impression FS
is less at low angles than it really is, especially if we
simplified and less accurate things like mininec grounds.
While everyone's experience varies, I have a 318 ft tower.
When I initially moved here I did hundreds of tests
comparing low dipoles (say 130 feet) to high dipoles, and to
a ~ 200 ft vertical with 100 200 ft radials. While there
were occasions where a dipole at 300 ft beat the vertical,
those conditions were only basically broadside to the dipole
(it had 20dB or deeper nulls off the ends) and they only
occasionally occurred. Most of the time it was a dead heat.
The lower dipole would be surprising sometimes when the
ionosphere was greatly disturbed, largely right at sunrise
or during severe geomagnetic storms.
I abandoned my high and low dipoles. That was a personal
choice made because the few times the low dipole was better
I was already so strong on the verticals ten dB more or less
would never make a difference anyway. I removed the dipoles
because they mostly sat unused.
This doesn't directly answer your question about surrounding
mountains, the only answer to that is if you would try both
a good vertical with a GOOD radial system and compare it to
a low antenna.
It won't make any difference if that low antenna is a loop
or a dipole, because the gain at every angle is virtually
the same as long as neither antenna has a problem affecting
efficiency. Use whatever makes you feel warm and fuzzy.
My best educated guess would go along with what Earl and
others have said, that even with surrounding mountains a
vertical would work wonders. ZL3REX is in that situation,
and when Rex went from a low full wave horizontal loop to an
Inverted L (with a GOOD ground system of at least a few
dozen radials) his signal level increased significantly. Rex
is the only one I know personally who had a situation like
you describe and spent a long time comparing antennas in a
blind A-B test.
73 Tom
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