Topband: Vertical vs. horizontal antennas at KC1XX

[John Kaufmann]

I would like to add some additional observations to the ongoing discussion
about horizontal vs. vertical antennas on 160.  At the KC1XX contest station
where I operate the low bands (160 and 80), we just installed two new
horizontal dipoles for 160.  For years, KC1XX has used a 3 element inline
vertical array that is described in an article I wrote back in 2002:
http://www.kc1xx.com/antennas/160_array.pdf.  (Note that my e-mail address
in that article is obsolete, so please use the e-mail address in this
message for any personal correspondence with me).  However, we have noticed
over the years that there have been times when the verticals don't seem to
be competitive, so we decided to try a horizontal antenna alternative to see
if that would help during those times.

 

I suspect the ground conductivity at the KC1XX location is not good, so that
needs to be considered in comparing antennas.  Vertical antennas suffer much
more over poor ground than horizontal antennas.  On 80m, KC1XX has
horizontally polarized delta loop arrays and a single vertical antenna that
is used for the "B" station on 80.  The vertical is always far inferior to
the delta loops, generally by 12-15 dB, which leads me to believe the ground
quality is pretty poor.  The delta loops have gain whereas the vertical does
not, but that alone does not explain the big difference between antennas.

 

The new 160 dipoles, installed just in the past 2-3 weeks, are very high.
One is broadside NE/SW and the other SE/NW, both with the apex at 200 feet.
The ends of the NE/SW dipole are at about 160 feet and the ends of the SE/NW
dipole are 130-140 feet.  KC1XX has a hilltop location with steep terrain
drop-off in multiple directions, particularly in the sector between
northeast and south.  To the east for example, the average downsloping
gradient is about 10% for the first 2000 feet and it continues down at a
somewhat shallower gradient for several thousand more feet.  As a result,
terrain modeling with the HFTA program shows a very large enhancement in the
dipole low-angle radiation, from 0 to 10 degrees, that is easily competitive
with a vertical array.  However, I don't have any data to know how useful
those very low angles are on 160.

 

The dipoles are high enough that they do exhibit significant directivity.
DX signals drop off a lot off the ends of the dipoles as you would expect. 

 

In the CQWW contest this past weekend, I spent a fair amount of time on 160
on both days and got to compare the vertical and horizontal antennas on many
DX stations.  Neither system was superior all of the time.  If I had to
generalize, which is a bit risky based on just two days of observation, I
would say that the vertical array is better, sometimes much better, on
average.  However, it varies greatly in specific situations.

 

When the band first opens to Europe before local sunset, the dipoles are
typically much better but that difference quickly diminishes after dark.
The first night in CQWW, the vertical array was generally 10-15 dB better
into Europe throughout the night but the second night it was almost a
toss-up where it was hard to see much difference between horizontal and
vertical.   Sometimes the dipole would be a bit better on a few stations and
other times the verticals had a slight advantage.

 

To the Caribbean, the dipole and verticals were roughly comparable, although
on some stations one antenna could be as much as 10 dB better than the other
for short periods of time.  Deeper into South America, the verticals were
usually better and it was generally the same on the few African stations I
heard. 

 

We worked a couple JA's, a UA0, and some VK's.  The verticals were superior
for those contacts.

 

What was very interesting was that sometimes I observed a long, slow QSB
where signals would start to drop down on the verticals while coming up at
the same time on the dipoles.  I suspect this is a polarization effect
rather than angle-of arrival because the dipoles and verticals both have
significant low-angle response where I would not expect one to outshine the
other if polarization were not a consideration.  This leads me to think that
feeding both horizontal and vertical antennas simultaneously through a
splitter might be a good option to have some of the time.

 

In summary, if I had to pick only one antenna system it would be the
verticals.  However, the high dipoles can easily hold their own at times and
it is good to have both options now.

 

73, John W1FV