User`s guide
noise sidebands
Modulation sidebands that indicate the short-term instability of the local oscillator
(primarily the first local oscillator) system of a spectrum analyzer. The modulating signal
is noise, in the local oscillator circuit itself or in the local oscillator stabilizing circuit, and
the sidebands comprise a noise spectrum. The mixing process transfers any local oscillator
instability to the mixing products, so the noise sidebands appear on any spectral component
displayed on the analyzer far enough above the broadband noise floor. Because the
sidebands are noise, their level relative to a spectral component is a function of resolution
bandwidth. Noise sidebands are typically specified in terms of dBc/Hz (amplitude in a 1 Hz
bandwidth relative to the carrier) at a given offset from the carrier, the carrier being a
spectral component viewed on the display.
nonvolatile memory
Memory data that is retained in the absence of an ac power source. This memory is
typically retained with a battery. Refer also to battery-backed RAM.
occupied bandwidth
A measure of the frequency bandwidth occupied by the carrier of a transmitter. It is
usually the bandwidth that includes 99% of the total mean carrier power, and is equivalent
to “99% power bandwidth”. It is measured by determining the lower and upper frequency
limits; where 0.5% of the total mean carrier power is below the lower frequency limit and
0.5% is above the upper frequency limit. Occasionally percentages other than 99% are
specified.
parameter units
Standard units of measure, which include the following:
Measured
Unit
Parameter
Name
frequency
hertz
power level
decibel relative to milliwats
power ratio
decibel
voltage
volt
time
second
electrical current
ampere
impedance (resistance) ohm
Unit
Abbreviation
Hz
dBm
dB
V
:
cl
peak detection mode
The analyzer state where circuits calculate the peak value of a displayed signal. This value
is determined by evaluating a series of measured values from an active trace.
peak detector
A detector that follows the peak or envelope of the signal applied to it. The standard
detector in a spectrum analyzer is typically a peak detector. MIL-STD EM1 measurements
usually call for peak detection. Refer also to quasi-peak detector and envelope detector.
percent amplitude modulation
A measure of the amount of amplitude modulation on a signal. The measurement value
is a comparison of the power in the modulation signal to the power in the signal being
modulated. Percent amplitude modulation can be calculated as follows, where
dB
is the
ratio of the power of the signal to the power of the amplitude modulation sidebands.
--dB
%AM
=
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Glossary-l 1