Mike,
I think the problem with elevated radials in 4 squares is the mutual
coupling and the necessity that the radial current and impedance be
equal. Otherwise the pattern is distorted.
Having measured my 8 125' elevated radials there is a significant (>2:1)
current imbalance in them due to several factors - towers, trees,
buildings, stuff in the ground, etc. I modeled this by having 8 sources
in the radials of the measured currents. My modeled pattern skew is
about 1db, so I am a bit skeptical of the CW for exactly balancing
radial currents for a monopole vertical. (see also N6LF modeling of
half circle radials).
After calibrating (essential!) my MFJ RF clamp on ammeter, the measured
antenna current and sum of radial currents were equal within 2%, so the
choke worked. The MFJ can only measure amplitude. Someday I will
investigate how the current phase is different in each radial referenced
to the vertical. Has anybody done that?
Grant KZ1W
On 12/21/2019 17:10, Mike Waters wrote:
Hi Frank!
Thank you for sharing this experience. This is interesting, because (as you
are probably aware of) no less a guru than N6LF published results showing
that with a single antenna, four ??/4 elevated radials were nearly identical
in performance to 120 on the ground. This is true *only* if RF was
prevented from either flowing into the lossy earth *or* back along the
feedline shield (thus detuning the elevated radials, since the shield would
try and act as a radial and couple to the lossy earth).
Was anything connected to ground at the feedpoints? And what type of coax
feedline choke unun did you use at the feedpoints? Perhaps there are
factors in an array vs. a single vertical that would explain your results,
but I can't think of any.
73, Mike
W0BTU
On Mon, Dec 16, 2019, 3:04 PM <donovanf@starpower.net> wrote:
Hi Mike,
Years ago my 4-square transmitting array used "gull-wing" elevated
radials sloping 45 degrees from the feedpoint at ground level to about
ten feet high.
When I replaced the radials with sixty 120-foot radials laid on the ground
I had to shorten the verticals by about five feet to maintain resonance,
suggesting that the current at the bottom five feet -- or so -- of the
verticals
was attenuated by the sloping radials in close proximity to the verticals.
As an aside, the performance of the array improved dramatically...
73
Frank
W3LPL
------------------------------
*From: *"Mike Waters" <mikewate@gmail.com>
*To: *"thoyer" <thoyer1@verizon.net>
*Cc: *"topband" <topband@contesting.com>
*Sent: *Monday, December 16, 2019 8:52:41 PM
*Subject: *Re: Topband: Temporary antenna suggestion for 160
CORRECTION
It was just pointed out to me that I neglected to mention that the
feedpoint on my 160m inverted-L was much lower than 10 feet high!
The tuner sits on the earth, and the two wires go straight up from that to
the insulator block holding the antenna and the radials, which is less than
4 feet high.
From that point, the two radials angle upwards at roughly 45?? (?) to nearby
trees, and level out at 10' high to the North and to the South all the way
to the ends. (The South radial zigzags back and forth since the distance
from the base to the neighbor's fence in that direction is less than 1/4
wavelength.)
I had photos of it online, but w0btu.com crashed. Looking for a place to
upload it to.
I hope this makes sense. Sorry for the lack of details below.
73, Mike
W0BTU
On Sun, Dec 15, 2019, 8:22 PM Mike Waters <mikewate@gmail.com> wrote:
Do the inverted-L, but use at least two 10' high 1/4 wave radials.
Do NOT use an RF ground rod, or any radials on or near the earth. Just
connect the coax shield to the junction of the radials and any remote
tuner. At that point a good choke balun is necessary.
Leaving out the choke or grounding the shield will result in very poor
performance.
73, Mike
W0BTU
On Sun, Dec 15, 2019, 7:04 PM thoyer via Topband <topband@contesting.com
wrote:
With only 9 more to go for DXCC on 160 and all of the recent posts about
how good the band has been recently "best in years....) I find myself
with
no
antenna for the low bands and cringing after each post on how good the
band has been.
...
Options - I have a 45' tower with TH6DXX, 6m and 2m yagis. I could
easily
string a makeshift inverted L with about 45' vertical and around 100'
horizontal. This I could string up in a few hours. the Horizontal
portion
would be pointed south. Not the best of configurations but that's what I
have to work with. ...
Tom
W3TA
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