As Brad suggests, the article by N6LF in QEX debunks a ton of traditional
lore. Especially regarding height above ground and length.
That article seems THE place to start for anyone considering an elevated
vertical build now.
It should be noted that the QEX article is all about a single vertical. The
extension from a single vertical to arrays where fields of overlapping or
joined elevated radials would be encountered has not been made with the same
level of experimental confirmation. And the usual references like ON4UN's
book are a bit non-specific by comparison as well.
73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie
-----Original Message-----
From: Brad Rehm
Sent: Friday, March 01, 2013 11:38 AM
To: Eddy Swynar
Cc: topband@contesting.com
Subject: Re: Topband: Elevated Radials
Eddy,
If you haven't already, you might want to take a look at Rudy Severns'
site (http://www.antennasbyn6lf.com/). A bit of reading will answer
some or most of your questions. It's been a few years since I studied
his material--the 160m inverted-L I build then embodied many of his
findings and suggestions. As I remember, he found very little
difference in the performance of radials an inch off of the ground and
radials 10 feet in the air.
As for the appropriate number, you can use two if you won't mind
having a less than circular pattern. The problem with having two,
four, or even eight is that it's more difficult to distribute current
among them. I use four radials elevated ten feet above ground. I've
never measured current in each of them, but I have noticed that the
antenna does better in some directions than others.
As for the optimum height... I've built elevated radial antennas with
the radials 15 feet above ground. My minimun height would be 10 feet,
which is high enough to avoid garroting my XYL when she mows the field
with our tractor. The one inch height that Rudy mentions resolves a
technical issue, but it's impractical from the point of view of the
guy who has to maintain them.
I don't connect the ground rod to the base of the antenna, because I
understand that an earth ground at this point would affect the pattern
and make it change behavior seasonally. The antenna's fed with a
2.23:1 balun, which provides a near 1:1 match to 50 Ohm coax and a DC
connection from the vertical element to the coax shield. The ground
rod wire comes up the post on which it's mounted and extends to within
1/16th of an inch of the 4-gauge wire ring to which the radials are
connected. The coax is connected to the antenna switch about 200 ft
away and attached to the ground system there. (The entire run of coax
is buried in PVC conduit.)
Just a few thoughts....
Brad
KV5V
On Fri, Mar 1, 2013 at 8:51 AM, Eddy Swynar <deswynar@xplornet.ca> wrote:
Hi Guys,
Forgive me, please, if I'm re-hashing a bit of the "...same-old, same-old"
here, but I am really curious as to any "real world" experiences that
might be out there in the matter of elevated radials, vs. those that are
simply laid atop the ground...
My arthritic knees here are making the chore of rolling, & unrolling, my
seasonal 24-radials-per-"L"-element radials (I have THREE of them here!)
just that, i.e. a VERY painful chore...and barring the possibility of
there being a new "bionic" knee replacement(s) in my future, pray tell me:
(A) Is it true that a couple of elevated radials are just as effective as
the "optimum" amount of buried ones...?
(B) What is the "ideal" number of elevated radials that one should use...?
(C) How many elevated radials are "just enough"...?
(D) How high should these radials be...?
(E) Would it be a requirement that I raise the feedpoints of my "L's" to
the same height as the elevated radials, or can I simply leave the bases
where they are now (at ground level) & simply slant the radials upward
with no effect upon performance...?
(F) Is it OK to bend the elevated radials to fit property allotments...?
(G) What is the desirable length of an elevated radial...?
(H) Should any existing connections to real earth at the base of the "L's"
(i.e. a ground pipe) be completed severed with a system of elevated
radials...?
This morning I happened to work a NJ station with elevated radials that
almost pegged the S-meter on my 751A---the short distance between us
notwithstanding, obviously something was working very well for him there!
Thanks in advance & my vy
~73!~ de Eddy VE3CUI - VE3XZ
_________________
Topband Reflector
_________________
Topband Reflector
_________________
Topband Reflector
|