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Noise
Nulling Interference and Noise
The
NCC-1
is not a noise blanker. The
NCC-1
is designed to reduce noise or interference before it
gets to the receiver by nulling the direction from which the noise is arriving. The
NCC-1
can be
effective on all types of noise, including interference (QRM) from unwanted signals. The
NCC-1
allows the user to continuously adjust both phase and amplitude when combining two antenna
inputs. The signal output to the receiver is the addition or subtraction of signals from two separate
receive antennas. Unwanted directional noise can be removed or unwanted signals can be cancelled.
Desired signals can be peaked or enhanced.
If noise is coming from several sources in different directions, satisfactory results may not be
achieved. Unlike conventional noise blankers, the phasing method of signal enhancement or
rejection does has several advantages.
Interference much stronger than a desired signal can be completely removed without affecting
the signal if it is arriving from a different direction than the desired signal.
The
NCC-1
can be effective with all types of interference and all modes.
Signals can be peaked instead of nulled with a flip of a switch.
Note:
Failure to follow guidelines outlined in sections below will often result
in reduced nulls or reduced enhancement of distant signals
Understanding Noise
Noise limits our ability to hear a weak signal on the lower bands. Noise is often an accumulation of
many unwanted signals. Noise from antennas is generally a mixture of local ground wave and
ionosphere propagated noise sources, although many locations suffer with dominant local noise
sources.
Noise is generated by randomly polarized sources. Noise polarization is filtered depending on the
method of propagation:
Noise arriving via the ionosphere
is randomly polarized. Noise arrives at whatever
polarization the ionosphere favors at the moment. Noise has the same ratio of electric to
magnetic fields as a "good" signal.
Sources within a few wavelengths of the antenna arrive randomly polarized. The noise does
not have a dominant polarization and it can either be electric or magnetic field dominant.
Local noise can also be random or directional in nature. Every effort must be made to locate
sources of noise that could be eliminated at the source. Dimmer switches, electric timers,
