An arrangement to measure cross talk properties in transmission lines wherein an interfering line is connected to a transmitter having an adjustable frequency and the far end of an interfered line is connected to a tunable superheterodyne receiver, and a voltage measuring system is provided at the output thereof. The reading data is obtained from the cross talk voltage measured during the tuning of the superhetertodyne receiver to the transmission frequency. A superheterodyne receiver tunable to the transmission frequency can be connected to the far end of the interfering line, and tuning of the superheterodyne receiver connected to the interfered line is performed as a function of the tuning of the superheterodyne receiver connected to the interfering line.
A method and an apparatus for measuring the bit error frequency in a cable caused by crosstalk from at least one disturbing pair to a disturbed pair at transmission of a 3-level coded PCM signal utilizes the fact that a PCM signal transferred on a pair and the disturbances superimposed on this signal by crosstalk from other pairs are mathematically uncorrelated. The amplitudes of the disturbances measured on the disturbed pair are sampled after equalization in a regenerator with a sampling frequency which equals the bit time frequency of the PCM signal intended for transmission on the pair. The number of detected sampling values whose magnitude exceeds a certain threshold value is a function of the estimated bit error frequency.
A pulse-based cable crosstalk measurement instrument provides near-end cross talk (NEXT) information for characterizing the performance of local area network (LAN) cable systems. Accuracy of the cross-talk measurement is enhanced by measuring and mathematically removing the cross-talk effects of the near-end connector. Accuracy of the cross-talk measurement is further enhanced by conducting the cross-talk measurement with pulses of differing pulse widths selected to have increased pulse energy in frequency ranges of interest. A composite cross-talk response using the individual cross-talk responses of the individual pulse widths concatenated together is created and then compared with an industry-standard pass fail limit to provide a pass-fail decision on a LAN cable test system under test.
A cable crosstalk measurement system provides fault diagnostic information to locates faults in addition to providing a crosstalk versus frequency function to test and troubleshoot LAN cables. In a preferred embodiment, a narrow pulse is introduced into one twisted pair of a standard LAN cable, and another twisted pair in the same cable is monitored for crosstalk signal coupling. A measurement system digitizes crosstalk signals using sequential sampling of repetitive signals to provide a waveform record that is a reconstructed equivalent time representation of a real-time crosstalk signal. A microprocessor performs a fast Fourier transform of the waveform record to provide crosstalk versus frequency information, while the waveform record is also examined for higher-than-acceptable amplitude levels to locate poor quality or faulty connectors and cables.
This invention relates to power control arrangements of digital subscriber lines. The invention controls parallel subscriber lines simultaneously in an organized way, based on the measurements of crosstalk conditions of the sub-scriber lines. Different crosstalk conditions are measured. The organized way to control the transmission power levels ensures that the crosstalk does not increase to an unacceptable level in each of the subscriber lines.
