Abstract: In order to evaluate the fidelity of a transmission line or other test object, a pseudorandom bit pattern is fed to the input end of that test object and is compared bit by bit with the pattern exiting at its output end. Since independent transmission errors are considered particularly relevant for this evaluation, in contrast to consequential errors following an initial error within a predetermined number of bit cycles, an error pulse emitted by the bit comparator causes the blocking of further error pulses for a selected time interval. The blocking may be effected by a retriggerable monoflop of adjustable off-normal period or by a presettable down counter.

Abstract: 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.

Abstract: To measure the level of test signals over a frequency range of variable bandwidth B, bounded by a lower frequency f' and an upper frequency f", these signals are heterodyned with a variable modulating frequency to produce a frequency spectrum encompassing the pass band of an intermediate-frequency filter of fixed bandwidth b.ltoreq.B, centered on a frequency f.sub.c. By periodically shifting the modulating frequency between a minimum value of f'-f.sub.c +(b/2) and a maximum value of f"-f.sub.c -(b/2), either continuously or in steps, the frequency range of bandwidth B is scanned by a window of bandwidth b transposed to the pass band of the filter as the midfrequency f.sub.m of the window varies in a sweep cycle between f'+b/2 and f"-b/2. The signal level in the output of the filter, integrated over the sweep cycle, is weighted with a corrective factor B/b.

Abstract: Bipolar signals used in binary or ternary data transmission, arriving at a receiving station, are periodically sampled under the control of sync pulses extracted from the incoming data train. The samples are rectified and stored on a capacitor whose voltage variations, upon rectification and integration, yield an indication of signal distortion during transmission. The average capacitor charge furnishes a feedback signal for keeping the voltage variations proportional to signal amplitude. A threshold circuit prevents the sampling of zero or near-zero voltages with ternary signaling.