Semi OT: vertical wire antennas

[Edward R Cole]

Lew,

I use a 43 foot high inverted-L on 500-KHz.  The top hat is 130-foot
long.  I have three parallel vertical wires and two horizontal wires
(tied together at base top and end).  I get a working bandwidth of
about 495-502 KHz with this extremely short antenna (4.6% of a
quarter wavelength).  the wires are insulated #12 solid copper-clad.
http://www.kl7uw.com/600m.htm

But a single wire will work as well since you are using a tuner at
the base.  My vertical wires stand off from a 50-foot Rohn-25 tower
by about 3-4 feet and does not seem to affect the radiation.  I would
not run the wire on the surface of the tree as wet wood will detune
it.  A few feet should be fine.

I use a HB base coil to ground and feed the coil 2-1/2 turns up from
the ground end with coax.  I have four ferrite beads on the coax to
decouple common mode radiation.  The coax runs across the ground to the shack.

I use a novel kind of ground plane:  Four runs of 2-foot wide chicken
wire laying on the surface of the ground - two are 50-foot long and
one is 70-foot, the fourth radial is the shield of my 120-foot 1-5/8
inch Heliax VHF transmission line which is tied to ground posts at
each end.  I do have to roll up the chicken wire for mowing in the
summer, but that only takes a few minutes.  I hold the wire down
using some concrete blocks as ballast.

I have read Rudy's QEX article and if you read it he found that 8
radials did pretty good so you might start there and add more if you
can later to see if that has a noticeable improvement.  BTW Rudy is a
member of our ARRL 600m Experimental Group, callsign WD2XSH/20.

So your plan using a wire vertical+ tuner at the base (ground with a
rod and radials) should work pretty well.  If you try the chicken
wire radial idea they should work at 30-feet as their width shortens
their electrical length.

My approach to antennas is try it, make notes, and change it if you
think it needs it.  I am in the process of that with my 16-foot eme
dish (re-engineering for making it more robust to withstand 65-mph winds).

73, Ed - KL7UW, WD2XSH/45

------------------------------
Message: 25
Date: Sun, 19 Dec 2010 16:21:27 -0800
From: Lew Phelps K6LMP <[hidden email]>
Subject: [Elecraft] Semi OT: vertical wire antennas
To: Elecraft Reflector <[hidden email]>
Message-ID: <[hidden email]>
Content-Type: text/plain; CHARSET=US-ASCII

I'm currently running my K3-10 into a 40 meter horizontal loop
antenna, mounted on my roof about 35 feet above ground. It's
impractical to use on 80, and has a very high angle of radiation on
40 and 20 meters.

So, I'm thinking of replacing it with a 43' wire vertical. Yes, I
know it needs a wide-range tuner, because it's non-resonant on any
ham bands. I already have that. And I know that it needs a 4:1
balun.  I can make that.

I have three questions for the group.

1. Is there any reason to expect that a wire vertical will perform
significantly differently than one made from aluminum tube (e.g.  2"
OD at base)?  EZNEC modeling shows  a slightly lower gain for a wire
antenna, but not significant. Is this borne out in real life?

2. The available grassy yard space where the antenna would be
installed would permit a maximum straight-line radial run of
approximately 30 feet, well under the desired length of 58 feet for
operation on 80 meters.  Would it affect antenna performance if the
radials were laid out in a series of Z jogs rather than in straight lines?

3. The antenna would be suspended from a large sycamore tree. Will it
make any difference in performance if I run the vertical right up the
side of the trunk, as contrasted with suspending it from a limb at
some distance (e.g. 5 - 10 feet) from the trunk?

Thanks,

Lew K6LMP







73, Ed - KL7UW, WD2XSH/45
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