Ceyear 4051 Series, Руководство пользователя

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4. Operating Instruction
4.2 Advanced operation guide
136
Fig. 4.53 Best position for time gate
The best measurement results are able to be obtained if the gate is generally set in the slight delay position of
the signal of interest, namely, within the interior area of signal of interest, but not extending to the pulse edge
or signal transition zone. Before the measurement of gate time, the SUT is set to the max value to provide
enough time for the resolution bandwidth filter of the analyzer to reach the stable status. In such case, the
slight delay position of signal of interest means the allowed SUT =4/resolution bandwidth. For instance, if the
filter of 1kHz is used for the measurement, the minimum SUT will be 4ms.
It should be noted that the signal is not the RF pulse but a specific periodic modulating signal, which
continuously effects on the full power or works when the pulse is low. For specific applications, adjusting the
gate position ensures enough SUT (not for the alternating process of other signals, e.g. The pulse edge or
transition zone). Proper selection of gate delay and gate width may achieve the best signal-to-noise ratio.
For the spectrum measurement between two pulses, there shall be enough SUT after the pulse ends and before
the Gate On so that the resolution bandwidth filter can fully discharge for the pulse high level to measure the
low level signals between pulses.
5) Effect of resolution bandwidth and video bandwidth
The resolution bandwidth value is determined by the gate position. It takes a long setup time for the small
resolution bandwidth, because the resolution bandwidth filter needs enough time to charge prior to the arrival
of the gate, where the SUT refers to the period between the gate arrival and the signal stability. As shown in
Fig. 4.54.
Fig. 4.54 Charging effect of resolution bandwidth filter
The resolution bandwidth filter is a band-limited device, so it will take a certain time for response and
condition change. When the Series Signal Analyzer measure the pulse signal, the filter needs a certain time to
fully charge.
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The SUT must be over the charging time of the filter.
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Setup time (SUT) > (4/Resolution Bandwidth).