incidental FM

Undesired frequency modulation on the output of a device (for example a signal source or an amplifier) caused by or, incidental to, some other form of modulation, such as amplitude modulation.

input attenuator

An attenuator between the input connector and the first mixer of an 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 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 5062. For some systems, such as cable TV, 750 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:

fl~f2,2xfl~f2,2xf2ff~,3Xf~f2xf2, andsoon

Glossary-13