W3HEM DE K3RA

Date: 1/16/2003  1:18 PM

Vertical and Horizontal Polarization with EZNEC or "How I Spent My
Lunch Hour"

Some More EZNEC Results Regarding The Advantages of
Horizontal Antennas over Verticals

After my presentation at the club meeting, I discovered that EZNEC has an
"Average Gain" calculation.  This title is a little misleading, but
essentially it averages the gain in all directions, and if there are no
losses due to wire loss or ground losses, the average gain should be 1.0
(or 0 dB).  This number provides a quick check of the "efficiency" of the
antenna above real grounds and/or with real conductors.

I mention this because we were talking about vertical antennas versus
horizontal antennas.  I looked at the "average gain" for a vertical dipole
above a variety of grounds compared to a horizontal dipole at about the same
average height above the same grounds.  I got the following results:

AVERAGE GAIN in dB (note, all are negative, meaning LOSS)

Pretty striking, huh?   Over average ground, 75% of the power you put into a
vertical is warming the worms!  Now you know why we don't mount our yagis
vertically for weak signal work.

For DX, unless a horizontal antenna is low to the ground with a resultant
very poor low angle pattern, it is likely to out-perform a vertical over
ground other than salt water.  For  high angle radiation for
short-to-moderate skip, the low horizontal dipole will crush the vertical.
(To work Sweepstakes at my old QTH, I put up a 40 foot high 80 meter dipole
which, for stateside,  was usually 3 or 4 s units better than my vertical
dipole array on 80 meters.)   I should comment that putting up a vertical
array, with gain in a preferred direction or directions, can compensate for
these reflection losses and outperform a "not too high" horizontal dipole
for DX.

The above results are essentially unaffected by radials.  The ground out
many wavelength is involved in these reflection losses, while the ground
close-in is not that important.  Radials ARE important for vertical antenna
efficiency, but they  only make a significant difference in that they can
greatly reduce the resistive losses at the feed point when feeding an
antenna against ground at a current loop (like a 1/4 wave vertical).  In the
case above, I used a vertical half wave dipole fed in the center, so radials
would not affect the losses significantly.

On 160, verticals are the only reasonable choice for getting a low angle of
radiation.   A dipole up 1/4 wave (130 feet on 160) shoots almost everything
nearly straight up in the air--so despite the reflection losses (lower
average gain) of verticals, they are still much better on 160 at the low
angles needed for DX..  The same is true on 80 for us mere mortals.
However, on 80  W3LPL uses horizontally-polarized cubical quads at an
average height of about 160 feet ( tops at about 200 feet), and he is on
high terrain, so the effective height is probably even greater (They are
incredible!!!).   Even on 40 meters, if you can't get your horizontal
antenna up about 1/2 wave or so, you are better off with a good vertical
(either one which is not fed against ground or one with a good radial
system).  Remember that EZNEC does not take into account terrain.  If you
are on a hill that slopes downward for many wavelengths in the direction you
wish to go, the effective height of your horizontal antenna will be much
better than that calculated from the height above the ground directly under
the antenna--which means your low angle will be much better.

In a conversation on the air, Vaughn asked about long horizontal loop
antennas, so I modeled a couple.  They are efficient, since they are
horizontally polarized.  They have a very complex pattern (symmetrical) of
high gain lobes and notches.   The longer (in wavelengths) the sides are,
the more complex the pattern.  With sides of a wavelength or more, they tend
to have lobes in all directions, but with real ground under them, they favor
the directions opposite the feedpoint. So, on FD, the club should feed the
loop on the east side so that the radiation favors west.  They should be fed
with low loss line--preferable ladder line--as the SWR will vary enormously
from band to band.  I would imagine, in general, that loops are pretty
effective, and I have worked guys running these kinds of antennas with very
good signals. Height, of course, will improve the low angle for DX.

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