3-36
Making Time Domain Measurements
Gating
Figure 3-27 Gate Shape
Selecting Gate Shape The four gate shapes available are listed in Table 3-4. Each gate has a different passband
flatness, cutoff rate, and sidelobe levels.
The passband ripple and sidelobe levels are descriptive of the gate shape. The cutoff time
is the time between the stop time (−6 dB on the filter skirt) and the peak of the first
sidelobe, and is equal on the left and right side skirts of the filter. As shown in Table 3-4,
the minimum gate span is just twice the cutoff time because it has no passband. Always
choose a gate span wider than the minimum. For most applications, do not be concerned
about the minimum gate span, simply use the knob to position the gate markers around
the desired portion of the time domain trace.
Table3-4 Gate Characteristics
Gate Shape Passband Ripple Sidelobe Levels Cutoff Time Minimum Gate Span
Gate Span
Minimum ±0.10 dB −48 dB 1.4/Freq Span 2.8/Freq Span
Normal ±0.10 dB −68 dB 2.8/Freq Span 5.6/Freq Span
Wide ±0.10 dB −57 dB 4.4/Freq Span 8.8/Freq Span
Maximum ±0.10 dB −70 dB 12.7/Freq Span 25.4/Freq Span
Note: With 1601 frequency points, gating is available only in the bandpass mode.