Glossary—492/492P Service Vol. 1
Display Law. The mathematical law that defines the in
put-output function of the instrument.
NOTE
The following cases apply:
1) Linear—A display in which the scale divisions
are a linear function of the input signal voltage;
Input Impedance.
terminal.
The impedance at the desired input
NOTE
Usually expressed in terms of VSWR, return loss, or
other related terms for low impedance devices and
resistance-capacitance parameters for high imped
ance devices.
m
m
m
w k
t k
m
m
I i
2) Square law (power)—A display in which the
scale divisions are a linear function of the input sig
nal power;
3) Logarithmic—A display in which the scale divi
sions are a logarithmic function of the input signal
voltage.
Dynamic Range. The maximum ratio of the levels of two
signals simultaneously present at the input which can be
measured to a specified accuracy.
Display Dynamic Range. The maximum ratio of the lev
els of two non-harmonically related sinusoidal signals each
of which can be simultaneously measured on the screen to a
specified accuracy.
Gain Compression. Maximum input level where the
scale linearity error is below that specified.
Spurious Response. A response of a spectrum analyzer
wherein the displayed frequency does not conform to the
input frequency.
Hum Sidebands. Undesired responses created within
the spectrum analyzer, appearing on the display, that are
separated from the desired response by the fundamental or
harmonic of the power line frequency.
Noise Sidebands. Undesired response caused by noise
internal to the spectrum analyzer appearing on the display
around a desired response.
Residual Response. A spurious response in the ab
sence of an input signal. (Noise and zero pip are excluded.)
TERMS RELATED TO DIGITAL STORAGE
FOR SPECTRUM ANALYZERS
Digitally Stored Display. A display method whereby the
displayed function is held in a digital memory. The display is
generated by reading the data out of memory.
Digitally Averaged Display. A display of the average
value of digitized data computed by combining serial sam
ples in a defined manner.
Multiple Display Memory. A digitally stored display hav
ing multiple memory sections which can be displayed sepa
rately or simultaneously.
Clear (Erase). Presets memory to a prescribed state,
usually that denoting zero.
Save. A function which inhibits storage update, saving
existing data in a section of a multiple memory (e.g.,
Save A).
View (Display). Enables viewing of contents of the cho
sen memory section (e.g., "View A” displays the contents of
memory A; "View B" displays the contents of memory B).
Max Hold (Peak Mode). Digitally stored display mode
which, at each frequency address, compares the incoming
signal level to the stored level and retains the greater. In this
mode, the display indicates the peak level at each frequency
after several successive sweeps.
Scan Address. A number representing each horizontal
data position increment on a directed beam type display. An
address in a memory is associated with each scan address.
REV AUG 1981
A-3
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