Ceyear 4051 Series, Руководство пользователя

Страница: 731 / 751

Appendix
Appendix A Terminology
717
of the detector output and the displayed trace is smoothed. The degree of such average or smoothing is
associated with the video bandwidth and the resolution bandwidth.
The video average is done point by point during several sweep operations. At each point, new measured data
and previous data are averaged together and average values of several measurements will be centrally
displayed. The video average function is only used in the signal/spectrum analyzers with digital display and
the average values depend on the sweep times selected by users. In average algorithm, one weighting
coefficient (1/n, n refers to current sweep times) is used as the amplitude value of the given point of current
sweep and another weighting coefficient [(n-1) / n] is used for previously saved average value. Such two
values will then be combined as current average value. After the specified sweeps are completed, the
weighting coefficients remain unchanged and dynamic average will be displayed.
In most measurement cases, the video filter is basically the same with the video average. However, they differ
in that the video filter a kind of real-time average function. When a signal drifting with the time is measured,
their difference becomes significant, leading to totally different measurement results. When the video filter is
used, each sweep may result in different average value; while the video average uses results of several sweeps
to obtain adequately averaged value. Therefore, the result got via the video average is very close to the actual
average value.
Input amplitude range
The power ratio (dB) of the maximum signal (usually the maximum safety input level) and the minimum
signal (display average noise level) measured at the input interface of the signal/spectrum analyzer. Such ratio
is always far larger the dynamic range to be realized in single measurement.
Input impedance
The terminal impedance presented by the signal/spectrum analyzer with respect to the signal source. The
impedance of the RF and microwave analyzer is usually 50 Ω. The standard impedance of some systems (such
as cable television) is 75 Ω. The degree of mismatch between the nominal impedance and the actual
impedance is expressed with VSWR.
Refresh mode
It is used to clear screen traces and sweep will restarted when the trigger condition is met. When the trigger
condition is met, new input signal data will be displayed.
Display range
The difference between the maximum signal and the minimum signal observed on the screen at the same time.
For the signal/spectrum analyzer with 10 amplitude scale intervals, its display range is scale coefficient * 10.
Average noise level display
When reducing peak-to-peak fluctuation of noise by decreasing resolution bandwidth with minimum
resolution bandwidth and input attenuation, the level observed on the screen of the signal/spectrum analyzer is
the display average noise level expressed in dBm. The display average noise level of the signal/spectrum
analyzer is equivalent to its sensitivity.
Linear display
The vertical scale on the screen is displayed in direct proportion to the input signal voltage. The graticule at
the bottom of the screen stands for 0 V and the top graticule stands for the reference level (depending on some
non-zero value of specific signal/spectrum analyzer). For most signal/spectrum analyzers, the scale factor
equals to the product derived by dividing the reference level with the number of divisions. In linear display
mode, the amplitude units of dBm, dBmV, dBμV, W and V can be used for the signal/spectrum analyzer.
Relative amplitude accuracy
Error of amplitude measurement The amplitude of one signal is compared with that of the other without
considering the absolute amplitude of either signal. Influence factors of amplitude accuracy include frequency
response, display fidelity, change in input decrement, IF gain, scale factor and resolution bandwidth.