Abstract: A method and apparatus for testing shield continuity are provided. In the method and apparatus, a transmitter transmits a first signal in common mode over a plurality of conductors of a cable or cabling installation having a shield. The first signal is transmitted in the common mode at a first end of the plurality of conductors. A receiver receives a plurality of second signals representative of the first signal at a second end of the plurality of conductors, respectively, and outputs data representative of the plurality of second signals. A processor receives the data representative of the plurality of second signals, determines a common mode insertion loss for the cable or cabling installation based on the plurality of second signals, determines, based on the common mode insertion loss, whether the shield is continuous or discontinuous and outputs data representative of whether the shield is continuous or discontinuous.

Abstract: A network analyzer includes a main unit and a physically separate remote unit. In at least one configuration, the main unit generates and transmits test signals through a device under test to the remote unit. Reference circuitry in the main unit uses signals from a local oscillator and an analog-to-digital ADC sample clock to produce reference signal data representative of the test signals as transmitted to the device under test. Receive circuitry in the remote unit produces received signal data representative of the test signals as received from the device under test, using the same signals from the local oscillator and ADC sample clock as used by the reference circuitry to produce the reference signal data. Comparison of the received signal data with the reference signal data indicates parameters of the device under test, including attenuation and phase shift in the test signals as caused by the device under test.

Abstract: A method and apparatus for testing shield continuity are provided. In the method and apparatus, a transmitter transmits a first signal in common mode over a plurality of conductors of a cable or cabling installation having a shield. The first signal is transmitted in the common mode at a first end of the plurality of conductors. A receiver receives a plurality of second signals representative of the first signal at a second end of the plurality of conductors, respectively, and outputs data representative of the plurality of second signals. A processor receives the data representative of the plurality of second signals, determines a common mode insertion loss for the cable or cabling installation based on the plurality of second signals, determines, based on the common mode insertion loss, whether the shield is continuous or discontinuous and outputs data representative of whether the shield is continuous or discontinuous.

Abstract: A network analyzer includes a main unit and a physically separate remote unit. In at least one configuration, the main unit generates and transmits test signals through a device under test to the remote unit. Reference circuitry in the main unit uses signals from a local oscillator and an analog-to-digital ADC sample clock to produce reference signal data representative of the test signals as transmitted to the device under test. Receive circuitry in the remote unit produces received signal data representative of the test signals as received from the device under test, using the same signals from the local oscillator and ADC sample clock as used by the reference circuitry to produce the reference signal data. Comparison of the received signal data with the reference signal data indicates parameters of the device under test, including attenuation and phase shift in the test signals as caused by the device under test.

Abstract: A method and apparatus for tuning crosstalk and return loss are provided. In the method and apparatus, a filter tunes return loss caused by a first external terminal and a second external terminal to compensate for a capacitive load induced by sizes of and a proximity between the first and second external terminals. The filter decouples the tuning of the return loss from tuning a magnitude and a phase of a crosstalk between a first transmission line network and a second transmission line network such that the return loss is tuned with minimal impact on the crosstalk.

Abstract: A method and apparatus for tuning crosstalk and return loss are provided. In the method and apparatus, a filter tunes return loss caused by a first external terminal and a second external terminal to compensate for a capacitive load induced by sizes of and a proximity between the first and second external terminals. The filter decouples the tuning of the return loss from tuning a magnitude and a phase of a crosstalk between a first transmission line network and a second transmission line network such that the return loss is tuned with minimal impact on the crosstalk.

Abstract: An equivalent time sampling system employs two clock frequency sources, phase locked, wherein an analog to digital converter sampling clock is derived from one source and a pulse generator clock is derived from the other. Choice of the clock frequencies determines minimum time step and the set of available time steps, and pulse repetition period determines the time step size, for equivalent time sampling. The system is suitably implemented in a time domain reflectometer, optical time domain reflectometry system, or other systems for obtaining time domain responses to a periodic stimulus of a system under test, with stimulus rate and the sampling intervals varying over a wide range.

Abstract: An equivalent time sampling system employs two clock frequency sources, phase locked, wherein an analog to digital converter sampling clock is derived from one source and a pulse generator clock is derived from the other. Choice of the clock frequencies determines minimum time step and the set of available time steps, and pulse repetition period determines the time step size, for equivalent time sampling. The system is suitably implemented in a time domain reflectometer, optical time domain reflectometry system, or other systems for obtaining time domain responses to a periodic stimulus of a system under test, with stimulus rate and the sampling intervals varying over a wide range.

Abstract: A method and apparatus to determine loss and length characteristics of a single optical fiber. An optical fiber to be tested is connected at its near end to the test port of an instrument having a light source, a detector, and a directional coupler. The far end of the optical fiber is terminated in a mirror. Light from the light source propagates down the optical fiber to the mirror, where it is reflected back to the detector. The results are processed by measurement circuitry and displayed.

Abstract: A system for determining FEXT and ELFEXT of generic cabling systems provides accurate measurements of these parameters by determining and removing the effect of the connectors at the respective ends of the link, thereby giving measurement values that correspond to the defined link, rather than including the crosstalk contributions of the connectors, which can be substantial.

Abstract: A pulse-based local area network (LAN) cable test instrument provides a measurement of the cross-talk characteristic of a LAN patch cord as a function of frequency in order to evaluate its relative performance and workmanship of assembly. A LAN cable test instrument applies a test signal in the form of narrow pulses to a selected transmission line of a LAN patch cord while the cross-talk response induced in another transmission line in the same LAN patch cord is measured and stored as a time record in digital memory. The near-end and far-end pulse responses are separated in the time record, leaving only the near-end pulse response. The LAN cable test instrument analyzes the near-end pulse response by performing a discrete Fourier transform on the time record to provide cross-talk versus frequency information. The same test may then be performed on the far-end end of the patch cord to obtain a complete test of the quality of workmanship at both ends of the patch cable.

Abstract: A pulse-based LAN cable test instrument that processes time-domain cross-talk measurement information in order to troubleshoot and quickly locate sources of cross-talk as a function of distance along the LAN cable system is provided. A pulse-response time record between a pair of transmission lines of the LAN cable system is first acquired. A series of steps to process the time-domain pulse response data in the time record are then performed to enhance the ability of the user to locate and troubleshoot the primary contributors to NEXT along any point of the LAN cable system. The pulse response data are first normalized as a function of distance from the LAN cable test instrument in order to compensate for losses along the LAN cable. Next, the pulse response data are integrated over the time record and the absolute value of the pulse response data is calculated to more clearly show the individual sources of cross-talk within the overall LAN cable pulse response.

Abstract: In accordance with the present invention, a pulse-based impedance measurement instrument is provided. A pulse generator repetitively generates a stimulus pulse to a device under test (DUT). A digitizer circuit, consisting of a sample-and-hold circuit, an analog to digital converter, and acquisition memory, repetitively samples the response voltage across the DUT to create a time record of the voltage as a function of time during a pulse response measurement. Each time record is operated on by a Fast Fourier Transform (FFT) which converts the voltage versus time information into voltage versus frequency information in a manner well known in the art. By measuring a set of calibration resistors with known resistance values to generate a set of complex calibration constants, the impedance measurement instrument provides measurements of complex impedance and return loss versus frequency of a DUT.

Abstract: A digital sampling circuit is providing for repetitively launching a series of stimulus pulses into a network under test and digitally sampling the resulting response signal. Enhanced time base accuracy of the repetitive sample is obtained using a pulse delay line in series with the pulse generator and a sample delay line in series with sample-and-hold (S/H) circuit. By summing digital samples obtained for the same time delay but using unique combinations of pulse delay line and sample delay line whose absolute time errors are combined differentially, the absolute time delay error contributed by both delay lines appears as a constant systematic error for any selected point along the response signal, allowing for highly accurate time intervals between selected points. This architecture is used to obtain an equivalent sampling resolution of 2 nanoseconds because each of the delay lines has two nanosecond steps.

Abstract: 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.

Abstract: 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.

Abstract: A pulse-based cable attenuation measurement system provides a measurement of attenuation characteristics of a cable over a wide frequency spectrum. A main test and troubleshooting unit of a cable test instrument applies stimulus signals via a selected one twisted pair in a LAN cable to a pulse receiver in a remote unit that in turn causes a pulse generator to produce a specified pulse of known amplitude and duration that is applied as a measurement pulse to a separate but adjacent twisted pair within the same bundle or cable. A measurement system analyzes the measurement pulse after it reaches the main unit, and provides attenuation versus frequency information to determine whether the amount of signal loss due to attenuation in the cable is acceptable or not.

Abstract: A frequency response stabilized amplitude modulation circuit includes a variable gain amplitude modulator producing an output signal having an amplitude proportional to a product of amplitudes of input carrier, modulating and gain control signals. An envelope detector generates a signal having an amplitude responsive to the modulation envelope of the output signal. A first difference amplifier produces the modulating signal input to the amplitude modulator in proportion to a difference between amplitudes of the envelope detection signal and an audio input signal. The modulating signal incorporates negative feedback to ensure the envelope amplitude of the modulated output signal tracks the audio input. A second difference amplifier provides the gain control signal input for the amplitude modulator in accordance with a difference between amplitudes of the modulating signal, scaled by a constant factor, and the envelope detection signal.

Abstract: An amplifying system and method produces a substantial reduction in the D.C. and even-order harmonics in an output signal by employing a first inverting amplifying stage cascaded with an attenuating stage which is cascaded with a second inverting amplifying stage. The electrical characteristics of each of the two inverting amplifying stages are substantially the same. The gain, in dB, exhibited by each of the amplifying stages is substantially equal to the attenuation loss, in dB, produced by the attenuator stage. Conventional components and fabrication techniques allow substantial attenuation of the D.C. and even-order harmonic components produced by the nonlinearities in the active devices of the amplifiers as compared to a single amplifier case producing the same gain A.