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Using an antenna at a lower height reduces corona cur­
rent—The electric-field gradient is smaller close to the wide
smooth surface of the earth. This is especially true when the
low antenna is surrounded by taller structures. Round, smooth
and insulated conductors are helpful, because they reduce
voltage gradient and resulting corona discharges. Vertical
antennas are particularly sensitive to precipitation static; they
have pointed ends protruding upwards towards the oppositely
charged sky. The corona also comes from the very high­
impedance antenna end, which aids in coupling power into the
receive system.
Beverages on the other hand, being near earth, will have
fewer corona discharge problems. They also have low surge
impedances. This means the low-current high-voltage arcs
transfer very little noise power into the antenna. Beverages are
thus quite resistant to precipitation static.
Quads are more resistant than Yagis because quads have
long flat sides with blunt lower- impedance high-current areas
towards the sky. Yagis have protruding high-impedance
pointed ends. Low-current arcs are not only more likely to
happen in Yagis, they are also better impedance matched to
the antenna! Quads have a reputation for being “quiet anten­
nas,” but this only applies to corona. For all other noises quads
are no better than any other antenna.

antenna is a much larger distance away. If however the noise
source is right on your street and the radiating power lines are
in front of your house, it is likely that all of this happens in the
near field of both the receive and sense antennas, and in that
case nulling will be impossible.
In all cases the sense antenna should ideally hear only the
noise and not the wanted signals, which means it must be fairly
close to noise source. And the sense antenna should be fairly
small.

1.4.3. Man-Made Noise
Local man-made noise is received several ways. When
the source is a modest distance (1 to 10 km) away, noise
arrives by groundwave propagation. If noise comes from just
outside or nearly outside the antenna’s Fresnel zone, it can be
eliminated with pattern nulls. The Fresnel-zone area is where
the pattern is not fully formed. The zone is related to array
size. It can extend a few kilometers with a very large array,
particularly one using broadside elements on low frequencies.
If the noise source cannot be eliminated using a directive
antenna, we often make use of so-called noise-cancellers to
solve the problem. If the noise source is from a single source
we can define a few solutions.

1.4.3.4. Propagated Noise
This noise generally sounds like a smooth hiss, even
though it is coming from hundreds or thousands of raspy or
harsh noise sources. Propagated noise is rarely, if ever, au­
dible in urban areas on 160 meters, since it is masked by harsh
local noises. Propagated noise is sometimes audible in quieter
directions of suburban areas on 160 meters, but not in “noisy”
groundwave directions or if a local dominant noise is present.
Propagated noise is often responsible for the entire noise floor
in remote rural areas. It is often possible to find the direction
of strong band openings by looking for highest propagated
noise, because the enhanced propagation can sum countless
noise sources for many thousands of km! Unfortunately, as
Tom, W8JI, says: “Propagated noise reduces the advantage
of super-quiet locations during the night.” Hearing propa­
gated noise is a good indicator of how quiet your location is
and how good your receiving system is. For example, the
winter season 160-meter daytime-to-nighttime noise level
increase at W8JI has been measured at 15 dB. This is in the
absence of thunderstorms within many thousands of miles.
While local man-made noise can often be nulled, propa­
gated noise is another story. Canceling propagated noise only
works with antennas of identical polarization and similar
patterns. The antennas must be close to each other, so they
receive signals in a constant phase and amplitude relationship,
with no space diversity. However, propagated noise con­
stantly changes phase, polarization and amplitude. Different
types of antennas in a canceling system respond differently,
making canceling impossible or very unstable. For any relief
from such propagated noise, it must arrive from a significantly
different direction than the desired signal.

1.4.3.1. Single-Point Radiation Far Source
Local noise arriving from one clear radiation point, even
if multiple sources, can easily be nulled. The antennas need
not be similar, but deep nulls require two antennas that both
“hear” the noise. The sense antenna should be placed closer to
and directly in-line with the noise source. The spacing can be
nearly any distance, but λ/4 or more is always best. There must
be a stable RF phase relationship between the noise received
in the main receive antenna and the noise-sense antenna. Since
local noise is received by surface or ground wave, the phase,
polarization, and amplitude are constant. This allows a stable
deep null to be obtained, using equipment such as the MFJ­
1025 noise canceller.
1.4.3.2. Distributed Radiation Source
Noise from a single source or multiple sources can be
fully nulled if the distance to the radiation area is large
compared to the length of the radiating area. This is true even
if the noise follows power lines and radiates from multiple
points or is from multiple sources. The sense antenna must
clearly and strongly pick up the noise. The ideal case is where
the sense antenna is very close to the source and the signal
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Chapter 7.pmd

1.4.3.3. Nearby Man-Made Noise
If the noise source is very close (in the near or induction
field), it becomes difficult or impossible to eliminate noise
through antennas arrays. In this case the problem must be
tackled in a different way, either by eliminating the noise
source or experimenting (trial and error) with various anten­
nas. Using a portable receiver or a fox-hunting (DFing) re­
ceiver for 160 or 80 meters, local sources can be easily found.
If the noise cannot be killed, such a single source noise, even
in the near field, can often be completely nulled out provided
the sense antenna is installed near the noise source, and the
main receiving antenna is located farther from the noise. It’s
obvious, however, that the best solution in this case is to “kill”
the noise source directly.

1.4.3.5. QRM
CW clicks, splatter, noise sidebands, etc is usually called
QRM, but it is just another form of noise. We do not deal with
QRM any different than the way we deal with other propa­

Chapter 7

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2/18/2005, 9:24 AM