[Elecraft] Semi OT: vertical wire antennas

[Ron D'Eau Claire]

Lew, the biggest difference between wire and tubing is the size of the
conductor. Thin conductors have higher Q and so narrower bandwidth,
necessitating somewhat more retuning as you move about the band. 

Many tests have shown that 1/8 wave radials - about 32 feet on 80 meters -
work FB. In the literature I've read there's almost no difference between a
1/8 and longer radial. It's more a matter of 'how many' than 'what length' -
especially when on (or in) the ground. 

I've not tried the antenna along the tree trunk idea myself, but again the
literature I've seen says there is no real difference. Even in the spring
when the sap is running strong the tree is much more a dielectric and not
much of a "conductor". That means there is some dielectric loss, especially
on the higher bands, but how much I've never seen quantified. 

Another approach to efficiency might be an "inverted L". I had to forego my
favorite center fed doublet using open line at this QTH because, while I
have plenty of room, > 100 large trees on the property limit my wire run to
only one direction from the "shack". So I use an Inverted L here about 130
feet long. It goes vertically 40 feet or so and then horizontally. The house
is on a knoll that drops off quickly within a half wave on 80 so the
effective height on 80 is more like 70 feet. The pattern is a strong mixture
of horizontal and vertical radiation that works very well. I get consistent
599's from Oceania at 100 watts (but I am only a few hundred yards from the
Pacific surf in Oregon ;-). I don't use a balun, but bring the end of the
antenna into the tuner in the shack. Yes, I can light up neon bulbs anywhere
near the tuner, especially on 80 where there's a voltage loop at the tuner,
but have no RFI problems. 

The fairly high feed point impedance on all bands from 3.5 MHz and up means
it's pretty well 'ground independent' and suffers little loss in efficiency
from not having an extensive ground system. I do tie to the mains safety
ground (underground utilities) with a short fat lead direct to the meter box
just outside the shack wall to keep RF voltages on the equipment low. 

Ron AC7AC

-----Original Message-----

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