incidental frequency modulation when limited by "incidental
Center frequency (radio frequency or intermediate fre-
quency)-That frequency which corresponds to the center
frequency modulation" (in units of Hz).
of the reference coordinate.
Phase Lock-The frequency synchronization of the local
oscillator with a stable reference frequency.
Center frequency range (radio frequency)-That range of
frequencies which can be displayed at the center of the
Resolution-The ability of the spectrum analyzer to re-
reference coordinate. When referred to a control (e.g., Inter-
solve and display adjacent signal frequencies. The measure
mediate Frequency Center Frequency Range) the term indi-
of resolution is the frequency separation (in Hz) of two equal
cates the amount of frequency change available with the
amplitude signals, the displays of which merge at the 3 dB
control.
down point. The resolution of a given display depends on
Dispersion (sweep width)-The frequency sweep excursion
three factors; sweep speed, dispersion and the bandwidth of
over the frequency axis of the display can be expressed as
the most selective (usually last IF) amplifier.
frequency/full frequency axis, or frequency (Hz)/division in
Resolution bandwidth-The -6 dB bandwidth (with
Gaus-
a linear display,
sian response) of the analyzer, with the dispersion and
sweep
Display
flatness-Uniformity
of
amplitude
over
a
rated
time adjusted for the minimum displayed bandwidth of
a CW
dispersion, The maximum variation in amplitude response
signal. Resolution and resolution bandwidth become
syno-
over the maximum dispersion is a measure of display flatness
nymous at very long sweep times,
(usually in units of dB).
Optimum resolution-The best resolution obtainable for a
Drift (frequency drift)-Long term frequency changes or
given dispersion and a given sweep time, Theoretically or
or instabilities caused by a frequency change in the spectrum
mathematically:
analyzer local oscillators. Drift limits the time interval that a
spectrum analyzer can be used without retuning or reset-
ting the front panel controls (units maybe Hz/s, Hz/C, etc).
Dynamic range (on screen)-The maximum ratio of signal
Optimum resolution bandwidth--The bandwidth at which
amplitudes that can be simultaneously observed within the
best resolution is obtained for a given dispersion and sweep
graticule (usually in units of dB).
time. Theoretically and mathematically:
Dynamic range (maximum useful)-The ratio between the
Optimum
dispersion (in Hz)
maximum input power and the spectrum analyzer sensitivity
resolution
(usually in units of dB).
sweep time [in seconds)
bandwidth
Frequency band-A range of frequencies that can be cov-
Safe power level-The upper level of input power that
ered without switching.
the spectrum analyzer can accommodate without physical
damage (usually in units of dBm).
Frequency scale-The range of frequencies that can be
read on one line of the frequency indicating dial.
Scanning velocity-Product of dispersion and sweep re-
petition rate (units of Hz/unit time).
Incidental frequency modulation (residual frequency modu-
lation)--Short term frequency jitter ar undesired frequency
Sensitivity-Rating factor of spectrum analyzer's ability to
deviation caused by instabilities in the spectrum analyzer
display signals.
local oscillators. Incidental frequency modulation limits the
usable resolution ond dispersion (in units of Hz).
1. Signal equals noise: That input signal level (usually
in dBm) required to produce a display in which the signal
Incremental linearity-A term used to describe local
level above the residual noise is equal to the residual noise
aberrations seen as non-linearities for narrow dispersions.
level above the baseline. Expressed as: Signal + noise =
Linear display-A display in which the vertical deflection
twice noise.
is a linear function of the input signal voltage.
2. Minimum discernible signal: That input signal level (usu-
Linearity (dispersion linearity)-Measure of the comparison
ally in dBm) required to produce a display in which the sig-
of frequency across the dispersion to a straight line frequency
nal is just visible within the noise.
change. Measured by displaying a quantity of equally spaced
Skirt selectivity-A measure of the resolution capability of
(in frequency) frequency markers across the dispersion and
the spectrum analyzer when displaying signals of unequal
observing the positional deviation of the markers from an
amplitude. A unit of measure (usually in Hz) is the band-
idealized sweep as measured against a linear graticule.
width at some level below the 6 dB down points. For ex-
Linearity accuracy, expressed as a percentage, is within
ample: 10 dB, 20 dB or 40 dB down.
X 100% where
is maximum positional deviation
Spurious response (spurii, spur)-An erroneous display or
signal which does not conform to the indicated frequency or
and W is the full graticule width.
dial reading. Spurii and spur are the colloquialisms used to
mean spurious response (plural) or spurious response (singu-
Maximum input power-The upper level of input power
lar) respectively. Spurious responses are of the following
that the spectrum analyzer can accommodate without de-
types:
gradation in performance (spurious responses and signal
compression). [Usually in units of dBm).
1. IF feedthrough-Signal frequencies within the IF pass-
Minimum usable dispersion-The narrowest dispersion ob-
band of the spectrum analyzer that are not converted in the
tainable for meaningful analysis. Defined as ten times the
first mixer but pass through the IF amplifier and produce dis-
2-3
