| 摘要 |
To measure the transmission characteristics of a signal line or other four-terminal network, a multifrequency test signal is fed through that network via a first channel to one input of a differential amplifier whose other input receives via a second channel a substantially identical comparison signal. A difference signal in the output of the differential amplifier, after rectification and possible filtering, is used for manual or automatic adjustment of an amplifier (or attenuator) and a delay unit in either or both channels until the magnitude of that difference signal is a minimum, its residual value indicating frequency-dependent distortions such as background noise or phase jitter not removable by broad-band adjustment of signal level and phase delay. The test signal, advantageously provided by a generator of the pseudorandom type, may be delivered to the second channel by that generator ahead of the four-terminal network to serve as the comparison signal; alternatively, the latter signal may be produced on the output side of the tested network by an identical generator under the control of synchronizing pulses extracted from the measuring signal traversing that network.
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