HP 8753E manual Sequence of Steps in Gating Operation

Gating

Gating provides the flexibility of selectively removing time domain responses. The remaining time domain responses can then be transformed back to the frequency domain. For reflection (or fault location) measurements, use this feature to remove the effects of unwanted discontinuities in the time domain. You can then view the frequency response of the remaining discontinuities. In a transmission measurement, you can remove the effects of multiple transmission paths.

Figure 6-75a shows the frequency response of an electrical airline and termination.

Figure 6-75b shows the response in the time domain. The discontinuity on the left is due to the input connector. The discontinuity on the right is due to the termination. We want to remove the effect of the connector so that we can see the frequency response of just the airline and termination. Figure 6-75~ shows the gate applied to the connector discontinuity. Figure 6-75d shows the frequency response of the airline and termination, with the connector “gated out.”

GATING OPERATION

Frequency

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Figure 6-75. Sequence of Steps in Gating Operation

Setting the gate. Think of a gate as abandpass filter in the time domain (see Figure 6-76). When the gate is on, responses outside the gate are mathematically removed from the time domain trace. Enter the gate position as a start and stop time (not frequency) or as a center and span time. The start and stop times are the bandpass filter -6 dB cutoff times. Gates can have a negative span, in which case the responses inside the gate are mathematically removed. The gate’s start and stop flags dellne the region where gating is on.

Application and OperationConcepts 6-141