Ceyear 4051 Series, User Manual

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Appendix
Appendix A Terminology
718
Preselector
The low-pass filter with tunable center frequency before the input mixer of the signal/spectrum analyzer. It is
used to eliminate multiple and image responses of the superheterodyne signal/spectrum analyzer and improve
its dynamic range. The preselector generally uses bands over 4 GHz.
Sensitivity
The capability of the signal/spectrum analyzer to measure signals with lowest level. The sensitivity is divided
into input signal level sensitivity, which produces input signal level about two times of average noise, and
equivalent input noise sensitivity, which the average level converted with externally generated noise to the
input interface. The best sensitivity can be obtained under the narrowest resolution bandwidth and the
minimum input attenuation and with adequate video filter. Influence factors of the sensitivity include input
attenuator, pre-amplifier, insertion loss of front-end devices, bandwidth of IF filter and noise sideband. The
video filter is unable to improve sensitivity, but it can enhance resolution capability and measurement
repeatability under low signal-to-noise ratio. The best sensitivity may conflict with other measurement
requirements. For example, when the resolution bandwidth is decreased, the sweep time increases; when
attenuation is set as 0 dB, the VSWR increases and the measurement accuracy decreases; when pre-amplifier
is increased, the dynamic range of the signal/spectrum analyzer is affected. Relation between the sensitivity
and the resolution bandwidth is as follows:
PdBm = -174 dBm + FdB + 10 LogB
Where:
PdBm: sensitivity of the signal/spectrum analyzer
FdB: noise factor of the signal/spectrum analyzer
B: 3 dB bandwidth of the signal/spectrum analyzer (Hz)
Noise Marker
A marker whose value indicates the noise level within 1 Hz equivalent noise bandwidth. When the noise
maker is selected, sample detector mode will be initiated and trace line points (the number of such points
depends on the analyzer) surrounding the marker will be averaged; obtained average value will normalize the
power within 1 Hz equivalent noise bandwidth.
Phase noise (noise sideband)
The oscillator of the signal/spectrum analyzer is used to convert input signals of different frequencies to IF.
The phase noise refers to the relative value (dBc/Hz) of the noise power and the carrier power within 1 Hz
equivalent noise bandwidth at certain frequency offset of the relative carrier. It indicates the level of short-
term frequency stability of the oscillator, which is caused by phase or frequency change. It is displayed among
signals of the oscillator as a bell-shaped noise characteristic. It affects the capability of the instrument to
measure phase noise of the tested signal as well as the sensitivity and the dynamic range of the instrument.
Harmonic mixing
LO harmonic ―generated‖ in the mixer is used in mixing to extend the tuning measurement range of the
signal/spectrum analyzer.
Gain compression.
When the input signal level increases, unit circuits of the signal/spectrum analyzer, including mixer and the
amplifier are working close to the saturation point. At such time, the input signal component will no longer
change linearly with the input signal and the displayed signal level is low due to gain compression. Usually,
the input level 1 dB (0.5 dB) lower than the output linear value offset is used to indicate 1 dB (0.5 dB)
compression point.
Normal detection
It is a display detection method for signal energy. Each displayed point corresponds to multiple detection
sampling data points of video signals in any part of the frequency span or the time interval indicated by such