Effects On Patterns; Site Selection In Relation To Noise Sources - DX Engineering DXE-RCA8C-SYS-2P Manual

Effects On Pattern
As far as pattern goes every directional array, no matter how constructed or designed, will always
interact with surrounding conductors. Adequate spacing is almost entirely dependent on electrical
characteristics of the surrounding conductors for a given style of receiving array.
For example, a given style array of similar dimensions from one company will be similarly affected
by surrounding conductors regardless of element design, for a given style of element. The effect on
pattern depends almost entirely on how much surrounding objects absorb and re-radiate signals, if
the undesired structure is in a null or peak of the receiving array, and how close the systems are in
terms of wavelength.
With so many variables involved, there is no optimum or minimum spacing for effects on pattern.
The best practice is to install the array as far as possible from tall conductors or noise sources, or
place potential problems in less frequently used directions. For best pattern, space the system as far
as possible from conductors that might be noise sources or re-radiate unwanted signals. One
wavelength or more is generally ideal, although adequate performance generally occurs with much
smaller spacing.

Site Selection in Relation to Noise Sources

Because the array is directional, use this example as a guide: If you have a noise source and if your
primary listening area is northeast, locate the array northeast of the dominant noise source. This
ensures the array is looking away from the source of noise when beaming in the primary listening
direction. The second-best location for the array is when the noise source is as far as possible from
either side of the array. If you look at patterns, the ideal location for the array is one that places
undesired noise in a deep null area. If this receiving array is in an area free of noise sources (power
lines, electric fences, etc.), locate the array so transmitting antennas and buildings are located in a
null direction or commonly unused direction.
Noise that limits the ability to hear a weak signal on the lower bands is generally a mixture of local
ground wave and ionosphere propagated noise sources. Some installations suffer from a dominant
noise source located close to the antennas. Noise level differences between urban and rural locations
can be more than 30 dB during the daytime on 160 meters. Nighttime can bring a dramatic increase
in the overall noise level as noise propagates via the ionosphere from multiple distant sources. Since
the noise is external to the antenna, directivity can reduce noise intensity.
Consider these things about noise sources:
 If noise is not evenly distributed, performance will depend on the gain difference between
the desired signal direction (azimuth and elevation) and gain in the direction of noise.
 If very strong noise comes from the direction of a receiving antenna null, improvement in
S/N ratio can be as much as 30 dB or more
 If noise predominantly arrives from the direction and angle of desired signals (assuming
polarization of signals and noise are the same) there will be no improvement in the signal-to-
noise ratio.
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