On Thu, 16 Sep 2010 09:12:36 -0700, Tom Osborne wrote:
>With a StepIR on top of a tower, wouldn't it make a difference which band
>the StepIR is tuned for for the sloper to work?
No, it does not matter, because the antenna elements are not connected to
the boom.
As to comaparing antennas -- MANY smart engineers among us have correctly
observed that the difference between two antennas is virtually ALWAYS
obscured by variations in propagation between two points, and by selective
fading (multi-path) over that path. I've just built two 160M antennas that
are wires sloping away from my 120 ft tower, driven against radials. One
antenna slopes to the east, the other to the west. In this configuration,
the tower acts as a reflector, providing roughly 6dB front to back. NEC
predicts a 3dB advantage as compared to my 86 ft tall top-loaded vertical
with 70 radials. NEC predicts that the antennas will have the same vertical
pattern.
For the last two weeks, I've been attempting to confirm that advantage. I
can CLEARLY hear the F/B by switching between the new E and W antennas, but
QSB is nearly always 15-20 dB over any skywave path, so I've not yet been
able to confirmed that predicted advantage by switching between new and old
antennas.
On the other hand, when I compared my 40M vertical dipole with my 100 ft
high horizontal 40M dipole, the advantage of the high horizontal was QUITE
obvious, no matter how many times I made the comparison.
I'm also in the process of hanging a 3-el inv vee wire yagi for 40M in my
tall redwoods at about 100 ft. It's wired so I can instanataneously switch
between it and a horizontal flat dipole that faces the same direction but
is about 20 ft higher. So far I have the driven element and the reflector
rigged, and it's got some gain. It's aimed to about 70 degrees. These
antennas DO have different vertical patterns.
Last night I was hearing stations from AF at a distance of about 7,800
miles at 60 degrees. Some signals are louder on one antenna, some on the
other, I'd estimate by 3dB or more. One was stronger on the Yagi, the other
on the dipole. I worked one of them.
73, Jim K9YC
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