User`s guide

input attenuator
An attenuator between the input connector and the first mixer of a spectrum analyzer (also
called an RF attenuator). The input attenuator is used to adjust the signal level incident
to the first mixer, and to prevent gain compression due to high-level or broadband signals.
It is also used to set the dynamic range by controlling the degree of internally-generated
distortion. For some analyzers, changing the input attenuator settings changes the vertical
position of the signal on the display, which then changes the reference level accordingly. In
Hewlett-Packard microprocessor-controlled spectrum analyzers, the IF gain is changed to
compensate for changes in input attenuator settings. Because of this, the signals remain
stationary on the display, and the reference level is not changed.
input impedance
The terminating impedance that the analyzer presents to the signal source. The nominal
impedance for RF and microwave analyzers is usually 5061. For some systems, such as
cable TV, 75Q is standard. The degree of mismatch between the nominal and actual input
impedance is called the VSWR (voltage standing wave ratio).
interface
The point at which different parts of a system interact. Also, the point at which operators
and instruments interact.
intermodulation distortion
Undesired frequency components resulting from the interaction of two or more spectral
components passing through a device having nonlinear behavior, such as a mixer or an
amplifier. The undesired components are related to the fundamental components by sums
and differences of the fundamentals and various harmonics. The algorithm is:
fi~fi,2xfi~f2,2xfiffi,3xfirt2xfi, andsoon
limit line
A test limit made up of a series of line segments, positioned according to frequency and
amplitude within the spectrum analyzer’s measurement range. Two defined limit lines
may be displayed simultaneously. One sets an upper test limit, the other sets a lower test
limit. Trace data can be compared with the limit lines as the spectrum analyzer sweeps. If
the trace data exceeds either the upper or lower limits, the spectrum analyzer displays a
message or sounds a warning, indicating that the trace failed the test limits.
limit,-line file
The user-memory file that contains the limit-line table entries. Limit lines are composed of
frequency and amplitude components that make up a trace array and this data is stored in
the file. The limit-line file feature is available on spectrum analyzers that are capable of
limit-line operation. Refer also to limit line.
limit-line table
The line segments of a limit line are stored in the limit-line table. The table can be recalled
to edit the line segments, then restored in the limit-line file. Refer also to limit line.
linear display
The display mode in which vertical deflection on the screen is directly proportional to the
voltage of the input signal. The bottom line of the graticule represents 0 V; the top line
represents the reference level. The reference level is a non-zero value characteristic to the
spectrum analyzer model. On the HP 140 series analyzers, select a specific scale factor in
volts per division. On newer models of spectrum analyzers, select the reference level. The
scale factor becomes the reference level value divided by the number of graticule divisions.
Although the display is linear, analyzers with microprocessors allow reference level and
marker values to be indicated in dBm, dBmV, dBpV, volts, and in some cases, watts.
Glossary-8