Ceyear 4051 Series, Руководство пользователя

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4. Operating Instruction
4.2 Advanced operation guide
133
Local oscillator: LO is a smart way for gating. It only sweeps LO when Gate is ON and passes through signal.
See Fig. 4.49 for the simple diagram of gating LO. It is observed that the Gate signal controls when the sweep
generator scans and when it passes through or shields signal. This enables that the Series Signal Analyzer only
sweeps when Gate is ON, that means, the Gate LO only sweeps LO and passes through signal when Gate is
ON.
Fig. 4.49 Working principle of gating LO
Gating Video: this form of gating may be thought of as a simple switch, which connects the input signal to the
Series Signal Analyzer. When the switch is ON (Gate ON), the video signal is allowed to pass through; and
the switch is off (Gate OFF), the signal is blocked. Under Gated Video, whether the gate is ON or OFF, the
Series Signal Analyzer measures signals and never stops sweeping. The working principle diagram of gating
video of 4051 Series Signal/Spectrum Analyzer is shown as Fig. 4.50. The Gate Switch is between the signal
pathway envelope detector and video filter, therefore is called as Gating Video. Since the Gate Switch is
behind the envelope detector, whether the Gate is on or off, the Series Signal Analyzer measurement path will
respond to the input signal; therefore, it is necessary to reduce the sweep speed to the extent that the Series
Signal Analyzer can measure input signal during Gate ON period, which results in certain limits for applying
Gated Video measurements. For this reason, in general, Video method results in slower measurement
compared with Gated LO and FFT.
Fig. 4.50 Working principle of gating video