Topband: FCP vs Gull Wing Elevated Radials

[Wes]

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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