HP 4935A, Руководство по эксплуатации и обслуживанию

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Model
Operation
1. measurement is a single number rating of the fidelity of a voiceband channel and is a
weighted measure of the total attenuation, phase distortion, and noise. The P/AR rating is derived by
comparing the P/AR of an ideal signal with the P/AR of the output signal of the system under test. The
measurement is most sensitive to envelope delay distortion and is also affected by noise, bandwidth
reduction, gain ripples, nonlinearities such as compression and clipping, and other impairments. P/AR is
simpler to understand than envelope delay because it is only one number instead of a curve. Also P/AR can
be measured in loop-around mode with only one instrument, unlike envelope delay. If the P/AR signal were
entirely undistorted, the rating would be while a circuit that causes a reduction in
the ratio has a rating of 80.
measurement provides little information about the nature of the fault condition in any
particular case. However, since P/AR is a figure of merit for the channel, it can be used as a benchmark for
future reference.
After other measurements are made and a channel is considered acceptable, the P/AR
rating can he recorded for future reference. In case of a suspected trouble on the channel, P/AR may be
measured first and he compared to the benchmark P/AR value. Deviations in excess of
P/AR units from
an initial P/AR value provides sufficient reason to suspect that some channel characteristic has changed
significantly.
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