China Electronics Technology Instruments AV3672 Series, User Manual

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Appendix
Appendix 2 Time Domain Measurement
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2) Cutoff time : the interval between the gate stop time (filter edge-6dB) and the first side lobe peak point.
3) Minimum gate span : twice of the cutoff time.
Schedule 2.3 Characteristic Indicators of Various Gates
Gate Shape Passband Ripple Side Lobe Level Cutoff Time Minimum Gate Span
Minimum ±0.10dB -48dB 1.4/frequency span 2.8/frequency span
Standard ±0.01dB -68dB 2.8/frequency span 5.6/frequency span
Width ±0.01dB -57dB 4.4/frequency span 8.8/frequency span
Maximum ±0.01dB -70dB 12.7/frequency span 25.4/frequency span
Fig. 2.13 shows the complete gate shape and the meanings of characteristic indicators.
1) T
1
is the gate span, equal to the difference of the stop time minus start time.
2) T
2
is the time between the passband edge and the point of -6dB, indicating the filter cutoff rate.
3) T
3
is the time between the point of -6dB and gate resistance band edge.
For all kinds of gates, T
2
is equal to T
3
. Both sides of the filter center are completely symmetrical.
Fig. 2.13 Schematic Diagram of Gate Shape
2.4.3.6 Minimum Gate Span
Each kind of gate is configured with a recommended minimum gate span for proper use. The minimum gate span is
determined by the limited cutoff rate and provided by the following equation. In this case, the filter passband is
equal to 0.
If the set gate span is smaller than the minimum value, the analyzer will have the following effects:
1) The gate shape is distorted, with no passband.
2) The gate is distorted.
3) The start time and stop time are not indicated correctly.
4) The side lobe level may increase.