Ceyear 4051 Series, User Manual

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Appendix
Appendix A Terminology
716
Signal/spectrum analyzer
The instrument used to effectively display each single spectrum component (sine wave) composing the time-
domain signal. Whether to retain phase information depends on the type of analyzer and relevant design
principles.
flatness
It corresponds to the variation in display amplitude of the measurement frequency range of the
signal/spectrum analyzer and indicates the corresponding relation between the signal amplitude variation and
the frequency.
Sampling detection
It is a display detection method for signal energy. The value displayed for each point refers to the
instantaneous value at certain time of the video signal at the frequency interval or time interval represented by
such point.
[Scanning time
The time it takes for LO tuning to pass the selected frequency interval. The sweep time directly affects the
timed used to complete one test, excluding the dead time after previous sweep completes and the next sweep
begins. When the span is zero, the horizontal axis only calibrates the time. When the span is not zero, the
horizontal axis calibrates both the frequency and the time. The sweep time often changes with the span, the
resolution bandwidth and the video bandwidth.
RF attenuator
The step attenuator between the input connector and the first mixer of the signal/spectrum analyzer. The RF
attenuator is used to adjust the signal level of the first mixer.
Residual frequency modulation
The inherent short-term frequency instability of the LO signal when there is no frequency modulation input. It
generally refers to the peak or its value with frequency dither in specified time interval within the test
bandwidth. The residual frequency modulation causes spectral line jitter, reduces actual resolution and affects
frequency readout accuracy of the signal/spectrum analyzer.
Video
The signal input from the detector of the signal/spectrum analyzer. Its frequency ranges from 0 Hz to far
beyond the frequency of the widest resolution bandwidth provided by the signal/spectrum analyzer and video
filter setting defines the final bandwidth of the video path.
[Video bandwidth
The bandwidth of the tunable low-pass filter in the video circuit of the signal/spectrum analyzer. The video
filter is the low-pass filter located behind the detector for defining the bandwidth of the video amplifier. It can
smooth the noise and is used to average or smooth traces. Besides, it can easily detect weak signals in noises.
Change of the video bandwidth does not affect the frequency resolution of the signal/spectrum analyzer, but
too narrow video bandwidth may lead to increase in the sweep time.
Video amplifier
The DC coupling amplifier located behind the detector of the signal/spectrum analyzer.
Video filter and video average
Since what the signal/spectrum analyzer displays is the measured signal plus its internal noise, video filter or
video average is required for the displayed signals in order to reduce the impact of such noise of the small
signals to be measured.
The video filter refers to the low-pass filter behind the envelop filter. When the video bandwidth is equal to or
smaller than the resolution bandwidth, the video circuit is unable to adequately respond to the fast fluctuations