I've been enjoying the intense debate over elevated radials with great
interest. In the past week I completed a two month project (in between
rainstorms); a 4 Square array for 160m. Just in time for the last major
contest of the season! The next step will be an attempt to increase
efficiency, by adding more elevated radials to each of the four radiators.
The project was inspired by K1KI/W1WEF's article in a recent NATIONAL
CONTEST JOURNAL, and a desire to be more competitive on 160m in contests.
K8DO's advice from my December post to this reflector determined the
initial elevated radial concept.
Briefly, the array is four, wire, top-loaded (80' vertical, sloping T 75'
long) radiators, fed at 8' above ground, each with TWO 133' radials which
slope up sharply (8' in 30" horizontal) from the feedpoints to 16'. The
radials then are suspended at 16', in a "box" configuration around the four
verticals, 130' on a side. Another pair of radials was just installed for
each radiator but are not connected yet. The radiators are suspended from
four rope catenaries extending from the top of a 135' tower (with two 40m
beams) to supports about 20' high, 250-300' from the tower. The whole
array, including radial supports, occupies 4 acres! Ground conductivity is
above average (not measured yet) and with all the recent rain, the water
table is about 5' below ground.
A Comtek hybrid combiner feeds the radiators with the same phase
relationships as K1ZM's system. The hybrid's 'dump' port is fed back to
the shack where I can monitor the unbalance dumped power. With the
radiators tuned at 1795 Khz, minimum dump power is 2% at 1840, and system
SWR less than 1.5:1 from 1800 to 1880 Khz. This week I'll connect the next
four pairs of radials and see what happens. Maybe the following step will
be 8 radials/vertical. A ground screen is not possible here for
agricultural reasons. Three of the four radiators are installed over my
grapevines. Another factor which makes modelling this situation unlikely,
is the miles of steel wire trellis' supporting the grapes. There are three
levels of wire, up to 6' above ground, not connected to each other, varying
from 200-350' long, extending the length of the property (1060') Don't try
this on your modeling software, Earl!
How does it work? So far (five days), on RX and reports from others, the
F/B is as advertised, 15-25 dB, even on stations closer than 500 miles. I
removed my 120' high inverted V from the support tower, so I don't have a
reference to compare it to. But it gets better reports from stations
worked recently with one radiator and gets thru the few pileups we have at
this late season better than with the one element I have used since the
ARRL CW contest in December. Very subjective, I know, but an early
observation none-the-less. The dipole will go back up at a lower height
this summer on another tower so I can compare signals and observe the
occasional high angle prop others report.
We all need to work with what we have, unless winning the lottery allows
starting from scratch with 640 acres on Salt Flats. I'm fortunate to have
10 acres to play on, but I wish the support tower were 200' high to allow
full size radiators, and I could locate the array a few wavelengths away
from the other antennas: multiple wire arrays for 80m, ten yagis for 40-10
and two beverages running right thru the 4 Square array (yes, I see the
effect of "rotating" the 4 SQ and hearing signal level changes on the
beverages.)
If anyone is interested in the mechanical details, let me know. Basically
the hardware came from Comtek(hybrid, phasing lines, current baluns) and
Home Depot (copper wire, PVC pipe, 10' 4x4 posts, concrete, etc.) Total
cost about $1500, but a yagi at 300' is beyond my means and energy level!
As I add radials, I might have something more to add to the GREAT RADIAL
DEBATE. Per W8JI and KM1H, I plan to do some F/S measurements from a
neighbor's site during the process.
CU in WPX SSB on 160(as KO6N). KK
.
Ken Keeler N6RO
Oakley, CA (50 miles East of SF)
KO6N (Radio Oakley Contester Club) and N6O(CQP 97)
Ex- K2EIU (1953), WA6DKF, W6PAA
N6RO@jazznut.com
Tel 510-625-2707 FAX 510-625-9403
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