I'm putting together a presentation which I think I'm going to call
"Working 160M with limited antennas," or something like that. I've
studied as much of the literature as I can find, including extensive
work by W2FMI, K3LC, N6LF, W8JI, and K2AV. My intent is to distill it
to the point that it isn't overwhelming and come up with some relatively
simple guidelines that guys can use to get on the air and have fun.
It seems to me that this work has been done in two forms -- careful
modeling, and careful measurements, but not all of it has been done on
160M. In some one-on-one discussions, Tom, N6BT has emphasized that
"the earth is fundamentally different on 160M as compared to 40M" where
much of N6LF's careful measurements have been done, so that Rudy's work
on elevated radials cannot be linearly scaled to result in guidelines
for 160M. I found radials at 4-6 ft ineffective on a new 160M antenna I
had rigged, and Tom suggested 16-18 ft as a minimum height. This summer
I raised them to that height, and preliminary tests suggest that they're
working fairly well.
One question I've not really seen a definitive answer to is the
effectiveness of elevated radials on a GROUNDED TOWER. I'm most
interested in any serious MEASUREMENTS -- the differences between a
great radial system and a mediocre is usually only a few dB, far less
than propagation and QSB, and, of course, quite dependent on ground
conductivity.
I will, of course, be showing Guy's folded counterpoise as a small lot
alternative, as well as noting W8JI's quite useful analysis of it.
I'm interested in the answer on a personal basis as well -- the new 160
antennas are wires sloping from a 110 ft tower, insulated from the
tower, fed at the base, one to the east, one to the west, fed one at a
time. The tower is a passive reflector, so loss in the radial system
matters. The tower is in a 4 ft cube of concrete, copper in the pour
bonded to the tower and to six 8 ft rods. I currently have 10 on-ground
#14 THHN radials on it, each 101 ft long (tuned to resonance with my
MFJ259B).
Please respond on the list -- I suspect others will be interested, and I
would appreciate the peer review.
73, Jim K9YC
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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