Ceyear 4051 Series, User Manual

Page: 149 / 751

4. Operating Instruction
4.2 Advanced operation guide
135
 Startup time (SUT) is 1.5ms.
2) Impact of scanning time
Although the scanning time does not affect the measurement results of gating LO, there may be
noncontinuous tracks for two LO intervals on the screen if the scan time is set too short, resulting in
increasing the scan time.
The scanning time has significant impact on the measurement results of gating video, so it is required to set
the parameters related to the scanning time corresponding to the measurement of time gate. It is recommended
that the scanning time should be set to be PRI× (track points-1) at minimum, and (PRI-τ) × (track points - 1)
for the actual scanning time.
3) Optimized bandwidth parameter
For the measurement of time gate, it is important to set proper bandwidth to observe the signal spectrum. To
better understand the signal characteristics, the max amplitude of the frequency point can be determined via
the max hold before opening the time gate. In order to optimize the measuring speed, the bandwidth can be
properly set to short to show the characteristics of the measured signal. For example, it is necessary to set the
bandwidth above 200kHz for the observation of the false signal within the frequency range of 200kHz.
4) Set the gate signal by the SUT and SD
Generally, the gate is required to be placed in the area of stable signal, instead of pulse edge or transition zone;
otherwise, it will interfere with the spectrum. The gate signal comes from the center of the pulse, and the SUT
is calculated after the width of about half a pulse. The setup time (SUT) refers to the duration prior to the
arrival of gate and after the signal stability. The SUT is required to set to be long enough for the resolution
bandwidth filter of transient burst. The signal delay (SD) refers to the time interval between the trigger event
and stable signal. If the trigger event and signal appear simultaneously, the SD will be 0 and the setup time
(SUT) is equal to the delay time, otherwise the SUT is equal to the value of gate delay time subtracting the SD,
as shown in Fig. 4.52.
Fig. 4.52 Positioning of time gate
The gate can be set at random, but some positions may provide more selections for the resolution bandwidth,
as shown in Fig. 4.53, the time Gate 1 and Gate 2 are extended to the pulse edge or signal transition zone,
resulting in some inaccurate measurements. Therefore, it is better to place the gate at 20%~80% of the pulse.
For Gate 3 and Gate 4, the best position is in the middle of the pulse, which makes a good match between the
SUT and gate width.