I guess I should have added "useful to me." At my location, I wouldn't dream of
having elevated radials less than 6 feet above ground. Running them through the
cactus and bushes could be just as difficult as on the ground, especially when
they need to be considerably longer. There also needs to be a common-mode choke
and lightning protection is more difficult and there are some mechanical
issues. I'm going to liberally quote from another of Rudy's papers:
https://rudys.typepad.com/files/qex-mar-apr-2012-1.pdf
"Among amateurs there's been a long running discussion regarding the
effectiveness of a vertical with an elevated ground system compared to one using
a large number of radials either buried or lying on the ground surface. NEC
modeling has indicated that an antenna with four elevated λ/4-radials would be
as efficient as one with 60 or more λ/4 ground based radials. Over the years
there have been a number of attempts to confirm or refute the NEC prediction
experimentally with mixed results. These conflicting results prompted me to
conduct a series of experiments directly comparing verticals with the two types
of ground systems. The results of my experiments were reported in a series of
QEX[1-7] and QST[8] articles (.pdf files of these articles are posted at:
www.antennasbyn6lf.com ). From these experiments I concluded that at least under
ideal conditions four elevated λ/4 radials could be equivalent to a large number
of radials on the ground.
Confirmation of the NEC predictions was very satisfying but that work must not
be taken uncritically! My articles on that work failed to emphasize how prone to
asymmetric radial currents and degraded performance the 4-radial elevated system
is. You cannot just throw up any four radials and get the expected results. I'm
by no means the first to point out that the performance of a vertical with only
a few radials is sensitive to even modest asymmetries in the radial fan[10,11,
12], the presence of nearby conductors or even variations in the soil under the
fan[9]. These can cause significant changes in the resonant frequency, the
feedpoint impedance, the radiation pattern and radiation efficiency. These
problems have been pointed out before but as far as I can tell no detailed
follow-up has been published. Besides the practical problem of construction
asymmetries, at many QTH's it's simply not possible to build an ideal elevated
system even if you wanted to. There may not be enough space or there may be
obstacles preventing the placement of radials in some areas or other
limitations. I think it's very possible that some of the conflicting results
from earlier experiments may well have been due to pattern distortion and
increased ground loss that the simple 4-wire elevated system is susceptible to.
As the sensitivity of the 4-radial system and it's consequences sunk into my
consciousness I began to strongly recommend that people use at least 10-12 or
more radials in elevated systems."
Based on the foregoing, I would be really reluctant to use a couple of gull wing
radials and call it good.
Wes N7WS
On 7/25/2019 12:37 PM, Richard (Rick) Karlquist wrote:
On 7/25/2019 12:01 PM, Wes wrote:
As to gull wing radials, Rudy Severns has looked at these too:
https://www.antennasbyn6lf.com/files/antenna_ground_system_experiment_5.pdf
Rudy's work is a treasure trove and I think I have everything he's written in
a folder on my hard drive. Believe me, considering how difficult it is to
lay radials in my cactus patch, if I thought gull wings would be useful I
would have used them. I don't.
Rudy shows gull wing down only 0.65 dB and comments that "radically
changing the radial geometry does not seem to have a major impact".
So I don't understand your remark that gull wings are not useful.
The reduction in drive impedance can be mitigated by increasing the
height by about 3 feet. I don't even have cactus but would never again
run radials on the ground now that Rudy has educated us.
Rick N6RK
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