18WuD2x

478 noise-current generator • noise-reducing antenna
noise-current generator A noise generator that
supplies a useful current. Compare NOISE-
VOLTAGE GENERATOR.
noise digit A digit (usually zero) generated during
normalization of a floating-point number. See
NORMALIZE.
noise diode A reverse-biased semiconductor diode
that produces a standard noise voltage.
noise elimination The nearly complete removal of
noise effects from a system. Noise can never be
eliminated altogether because the movement of
electrons and atoms generates some electrical
and thermal noise. However, in some digital systems,
the effects of noise can be almost totally
overcome. Compare NOISE SUPPRESSION.
noise equivalent power Abbreviation, NEP. The
power that produces an rms signal-to-noise ratio
of 1 in a detector.
noise factor For a circuit, especially a communications
receiver or weak-signal amplifier, the ratio
R 1 /R 2 , where R 1 is the signal-to-noise power ratio of
an ideal circuit, and R 2 is the signal-to-noise ratio of
the circuit under test. Compare NOISE FIGURE.
noise figure The NOISE FACTOR of a circuit, expressed
in decibels. If N is the noise factor expressed
as a ratio, then noise figure N dB can be
determined by N dB = 10 log 10 N.
noise filter A filter designed to suppress noise that
would otherwise enter an electronic circuit (e.g., a
power-line noise filter).
noise floor 1. In a receiver, the level of noise in microvolts
that determines the weakest signal that
can be heard or accurately received. 2. In a spectrum
analyzer, the level of noise that determines
the weakest signal that will be visibly displayed.
noise generator A device for generating precise
amounts of noise voltage for test purposes.
noise grade 1. The relative level of radiofrequency
background noise, over all electromagnetic
frequencies, in a particular geographic
location. The noise grade is generally lowest
near the poles and highest near the equator.
2. The mathematical function of relative electromagnetic
noise intensity versus latitude and
longitude.
noise immunity The degree to which a circuit or
device is insensitive to extraneous energy—especially
noise signals.
noise-improvement factor Abbreviation, NIF. For
a radio receiver, the ratio SN i /SN o , where SN i is
the input signal-to-noise ratio and SNo is the output
signal-to-noise ratio.
noise killer 1. See AUTOMATIC NOISE LIMITER.
2. See NOISE FILTER. 3. See NOISE BLANKER.
noiseless alignment See VISUAL ALIGNMENT.
noise level 1. The amplitude of ambient electrical
noise generated outside an electronic system of
interest. 2. The amplitude of electrical noise generated
in an electronic system of interest. 3. The
intensity of ambient acoustic noise.
noise limiter See AUTOMATIC NOISE LIMITER.
noise margin In a binary logic circuit, the difference
between operating and threshold voltages.
noise-measuring set See NOISE METER.
noise meter An instrument for measuring acoustic
noise level. It consists essentially of a sensitive,
multirange voltmeter provided with a
microphone, amplifier, and attenuators. The meter
scale reads noise level directly in decibels.
Readable signals
Amplitude axis
Mike Amp. µΑ
Signals below
noise floor
noise floor, 2.
Frequency
axis
Noise
floor
Do not appear
in display
noise meter
noise power The power component of a noise
signal.
noise power ratio The ratio of noise power at the
output of a circuit (such as a receiver) to the noise
power at the input.
noise pulse A random short-duration noise burst
whose amplitude exceeds the average peak noise
level.
noise quieting In a radio receiver, the reduction
(in decibels) of background noise, with respect to
a signal of interest.
noise ratio See NOISE POWER RATIO.
noise-reducing antenna A receiving antenna having
a balanced transmission line and usually
some form of noise-balancing system for reducing
electrical noise picked up by the antenna.