Bruce,
You didn't state how long the fiberglass insulators are
which makes me suspect you have LONG continuous
lengths of GROUNDED guy wires around the tower.
Is that correct?
Isolated conductive guys need to be Less Than 0.3 WL
(Wave Lengths) at the highest frequency of concern to be
"invisible" to other antennas. For grounded conductors,
that would be 0.15 WL at the frequency of interest.
Are you familiar with long wire patterns?
A top loaded 180 ft vertical on 80M will act
as half of a current fed long wire with very
large lobes centered approximately 30+ degrees
from the tower. In other words, MOST of the
radiated energy will be at VERY HIGH angles
which is fine for domestic coverage but not
a very good solution for DX. There will be a
narrow low angle lobe also but with less
energy and coverage than a good single
1/4 WL vertical.
Another 80M vertical option is a K8UR style 4 square
using 4 V's hanging sideways off the tower. Again,
if you have LONG conductive guy wires, they will
most certainly interact with any vertically polarized
antennas around the tower.
IMHO, your BEST option for 80M is a rotary dipole
(or 2L Yagi) at the TOP of the tower, parallel to the
boom of your HF Yagi to minimize interaction.
Alternatively, a pair of inverted vees with the ends
pulled WAY OUT (120-150 degree apex angle) or
Horizontally Polarized Delta Loops at right angles
to each other is a good and cost effective solution.
The Delta Loop solution requires less land area
since the apex angle is only 60 degrees. The
bottom of an 80M delta loop will be approximately
80 ft below the apex which is still 100 ft for your
180 ft tower. If it were my tower, I would go with
a pair of horizontally polarized Delta Loops aimed
broadside at 60 / 240 and 150 / 330 degrees which
gives good coverage of the major population areas
of the world from the Eastern USA.
To determine where to attach the feed for 160M,
you can either model the system or experiment
by placing a tap wire (spaced a couple of feet from
the tower) at various levels and measuring the
impedance at ground level. I spent several hours
doing the latter to determine the 50 ohm point on
a 100 ft top loaded tower. Another solution would
be to simple run a 1/4 WL vertical wire from the
tower.
Tom N4KG
On Thu, 26 Dec 2002 "Bruce Snow" <wy8g@redbird.net> writes:
> In my backyard is my 180ft. tower 18 inches wide.10 ft. of mast pipe
> extend skyward from the crown of the tower
> and on top of the mast is 20 more feet of a 450mhz 8 bay folded
> dipole and hustler G7-220.All of my guy wires hit fiberglass guy
> strains at the tower so none of the guys electrically touch the
> tower.My ambition is to turn this tower into a 160/80 mtr
> vetical.Also on the mast pipe is a Mosley Pro-56.It seems the more I
> read the more confused it seems to me on where to tap the tower.Any
> ideas would be much appreciated.Thank you,73 from WY8G.Bruce
>
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