For most of the last three years, I have used an inverted-u dipole at 60 to
40' high, which has produced around 120 countries. I agree with Yuri VE3BMV
and Bill W4ZV's observations about high angle radiators, but here are a
couple of other bits of food for thought.
"Another fact which causes me to believe the radiation angle was high was
that my
Beverages (low angle antennas) ceased being as effective as the dipole
after my sunrise
for Pacific DX stations. (Bill W4ZV)."
I have a 500' Beverage running west to east. When I first put it up, I
thought something was wrong with it as stations I worked in the USA were
often virtually inaudible on it, while they were S5 - S7 on the dipole. As
Bill says, the answer is simply the signals were coming in at very high
angles. During the really good NA openings last season, 99% of the signals
fell into this category.
Note that this is simply how the signals actually arrived here - at what
angle and polarisation they were actually leaving the other end is anyone's
guess - I can't tell, for sure!!!
Yuri's point about polarisation changing as it leaves your antenna is
especially important - as is efficiency. Some of those loud USA signals
were using verticals, while some were on horizontals. My feeling is that
everyone I worked had a reasonably efficient (low earth loss) system,
probably over a fairly wide range of radiation angles.
Now, onto efficiency. Unless you have good ground or lots of half wave
radials - or both - it is difficult to get an efficient vertically polarised
antenna. Dipoles are an apparently easier option. However, vertical
antennas over poor soil are inefficent at very low angles, while dipoles
over poor soil are inefficent at very high angles (see ON4UN's book).
Over perfect ground, a dipole at 1/8 wave might have its peak signal at 90
degrees, but the signal at 45 degrees is only 3dB down from this... Over
less than perfect ground, maybe there is almost as good signal at 45 degrees
from the dipole, as there is at 90 degrees... With my struggles with
verticals here over a poor earth, producing a signal at 45 degrees that is a
mere 3dB down from a full size vertical is something I'd love to be able to do.
What I am trying to say is that under some poor ground conditions, a low
horizontal is a better - more efficient - low to medium angle radiator -
than a vertical. However, it is no good making assumptions - you have got to
try both types of antenna if you really want to find out what works best for
your QTH.
We are all operating over less than perfect ground, so our dipoles are less
good high angle radiators than we think they are (and better medium angle
radiators) - and our quarter wave verticals are probably worse low angle
radiators than we think they are, too.
My situation is the reverse of Bill, W4ZV's It is hard for me to get an
efficent vertical here, so I favour horizontal antennas. However, I still
like to have a vertical antenna, for those one to five per cent of occasions
when it works better than a horizontal.
PS Bill W4ZV - did putting a reflector under that dipole in Colorado help
with the DX signals?
Vy 73,
Steve, VK6VZ
During many, many tests with the VK gang (mostly on SSB such that I could
get quick
comparative reports at different times before and after my sunrise), here
is a summary
of what I observed:
1. Before sunrise (~1 hour to 10 minutes before), vertical was usually
stronger by 1-2 S units.
2. At sunrise (~10 minutes before to 5 minutes after), both antennas
were about equal.
3. After sunrise (~5 minutes to 40 minutes after), dipole was usually
stronger by 1-2 S units.
Another fact which causes me to believe the radiation angle was high was
that my
Beverages (low angle antennas) ceased being as effective as the dipole
after my sunrise
for Pacific DX stations.
Of course the dipole was also the stronger antennna for local (<500 mile)
contacts, but I
made many DX QSO's under unusual conditions with the dipole that would
not have been
possible with the vertical/Beverage combination. For example, after
sunrise to the Asia/
Pacific area (YB0ARA when he was in Jakarta, VK9XS on Christmas Island)
and sometimes
to Europe and Africa before Colorado sunset. I remember one QSO in
particular when I was
total darkness near 7Q7XX's sunrise. The East Coast obviously had a good
opening
but I could just barely tell he was there while listening on my Beverage.
The pileup died
down after his sunrise (around 0300 I recall) and I remembered to try
listening on the dipole.
He was weak but clear as a bell and I worked him on the first call for a
new one! I recall
later checking his exact sunrise time and our QSO was about 15 minutes
after his sunrise.
The bottom line to all of this is that a dipole or another good high
angle antenna does have
its place in your antenna arsenal, but think of it as a complement to a
good low angle
antenna which will be better 99% of the time. It's those 1% situations
that sometimes
make you glad to have a high angle system!
--
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