Hi. Richard
I've been following this thread -mostly for entertainment.
I've noted your postings re elevated radials to replace deteriorated buried
radial fields under broadcast towers. I'm familiar with the work and the
results. This work, of course was done by professional broadcast engineers
with significant instrumentation at their disposal. Of course, they also had
to measure the field intensity in the far field and file it with the FCC.
Their work seemed to show that, once we have installed 4 elevated 1/4 wave
radials we're reaching the point of "diminishing returns" and that little is
to be gained by increasing the number of radials beyond 4.
I'm sure you appreciate by now that there are a LOT of authoritative and
fervently held opinions that are spouted in this reflector without any
supporting data or results. And we "can't reason people out of positions
that they didn't arrive at through reason"!! Most hams do not seem to
appreciate that a 160m inverted -L with elevated 1/4 wave resonant radials
is, in fact, a ground-plane antenna, with the vertical radiator bent to make
use of available supports and should be considered and analyzed as such!
Nevertheless, there are a LOT of authoritative pronouncements like "as many
as possible" (elevated radials) or "as high as possible" (again for elevated
radials - and this only serves to reduce the effective height of the
high-current portion of the vertical radiator). Hams seem more inclined to
rely on apocrypha, and "hearsay" from folks that they consider to be
authoritative topband "gurus". These views, though passionately and
fervently held, generally are lacking of supporting data, and theoretical
support. They are entertaining, but not really helpful!
There seems to be something "mysterious" and "sacred" in the topband
community about "dirt"! About the only rationale that I can arrive at for
buried radials is if one is shunt feeding a grounded tower. If the vertical
radiator can be isolated from ground, then the elevated resonant radials
will do very nicely.
I ran 160m inverted Ls with resonant elevated radials for years - usually 3
or 4, but sometimes just two, and a couple of them had to be "bent" because
of lot limitations. With 500-600W I could be heard pretty much anywhere in
the world - VK6,3B8,ZL,ZS, KH6,.JA and "deep" Russians etc. from my lot in
NC. My problem was never being heard- it was HEARING!(I helped the hearing
issue a LOT when I put in some "Kaz" terminated loops that could be
accommodated on my city lot.) My radials were not very high 5-6 feet along
the property fence lies and one ran along under the eaves of my one-story
house because it was convenient. It all worked really well until Hurricane
Fran took down the tree that was supporting the far end of the inverted L
that was about 75 feet. Because of intervening hip replacement surgery and
a long recovery I haven't rebuilt it -yet. But have hopes and plans for this
summer.
Anyway, reasoning, or arguing, with topband hams about antennas is a lot
like having a religious or political discourse. Generally they seem to just
BELIEVE!
I do appreciate and value your posts on this reflector.
Best regards,
Charlie, K4OTV
Charles Cunningham Jr, PE
P.S. Elevated radial DO need to be high enough that we (or wildlife) don't r
un inti them
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Richard
Fry
Sent: Tuesday, March 05, 2013 6:45 PM
To: topband@contesting.com
Subject: Re: Topband: Elevated Radials
Guy Olinger posted:
>...The very same NEC 4.2 with raised quarter wave radials over routine real
>life ground made of dirt will show field intensities in the ground. (etc
>etc)
_______________
Sorry, but this is a misunderstanding/misuse of NEC for this situation.
The r-f currents flowing in the earth under and near elevated, horizontal
radials are NOT the source for the r-f currents flowing on those radials,
themselves. Those radial wire currents are supplied by the currents flowing
on the inside surface of the outer conductor of a coaxial transmission line
used to drive the monopole -- which is connected to the common point of
those elevated radial wires.
Elevated radials behave much differently than buried radials. In effect,
driving a vertical monopole against an even number of geometrically-
symmetric pairs of at least two elevated, horizontal wires used as a
counterpoise converts a base fed (unbalanced) monopole radiator into a
balanced radiator -- which neither needs, nor can use a structural
connection to the earth for most efficient system performance.
For proof of this, please study the measurements of a real-world system
using 4 x 1/4-wave elevated radials described in the link below, for/at
WPCI, 1490 kHz in Greenville, SC, and the rest of that paper.
http://www.commtechrf.com/documents/nab1995.pdf
RF
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