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envelope detector
A detector circuit whose output follows the envelope, but not the
instantaneous variation of its input signal. This detector is sometimes
called a peak detector. In superheterodyne analyzers, the input to the
envelope detector comes from the final IF, and the output is a video
signal. When we put the analyzer in zero span, the envelope detector
demodulates the input signal, and we can observe the modulating signal
as a function of time on the display.
error message
A message displayed on the screen indicating missing or failed hardware,
improper user operation, or other conditions that require additional
attention. Generally, the requested action or operation cannot be
completed until the condition is resolved.
external mixer
An independent mixer, usually having a waveguide input port, used to
extend the frequency range of those analyzers designed to use them. The
analyzer provides the local oscillator signal and mixer bias (if needed),
then returns the mixing products to the analyzer’s IF input.
FFT
The abbreviation for fast Fourier transform. It is a mathematical operation
performed on a time-domain signal to yield the individual spectral
components that constitute the signal in the frequency domain. Refer also
to spectrum.
firmware
An assembly made up of hardware and instruction code that are
integrated to form a functional set which cannot be altered during normal
operation. The instruction code, permanently installed in the circuitry of
the instrument, is classified as ROM (read-only memory). The firmware
determines the operating characteristics of the instrument or equipment.
Each lirmware version is identified by a revision code number, or date
code.
flatness
The displayed amplitude variation corresponding to the tuned frequency
range of the analyzer. Flatness of
f
1
dB
indicates that maximum and
minimum values of the analyzer’s frequency response are less than 2
dB
apart.
Glossary-9