Abstract: A spectrum analyzer (50) has a tunable trigger acquisition system (52) that includes a selectable trigger acquisition bandwidth. Sufficiently wide signal acquisition bandwidth is obtained by tapping into a high-frequency IF amplifier (54) signal and down-converting it to a moderate IF frequency for trigger extraction. A down-conversion local oscillator (62) is phase-lock-loop (64) tunable over a range of the high IF frequencies to allow extracting a time and frequency selectable trigger from the desired carrier signal frequency even if the spectrum analyzer is substantially offset in frequency from the desired carrier. The moderate frequency IF amplifier (66) includes a switchable bandpass filter (68) that provides adequate selectivity to detect triggers from a variety of signal types while rejecting unwanted signals such as adjacent channel CATV carriers that are often detectable when the measurement frequency is offset toward the channel edges.

Abstract: A non-interference method of determining the frequency characteristics of a cable television (CATV) system adds an RF test pulse to an RF video signal in the vertical interval between equalizer pulses. A gated receiver coupled to the distribution system receives the RF video signal only during the vertical interval and extracts the envelope of the RF test pulse, with the sync pulses being attenuated. RF pulses of different frequencies within each channel of the CATV system are used to determine the frequency characteristics of each channel.

Abstract: A cable television measurement system uses a modified spectrum analyzer for determining both carrier-to-noise and triple beat ratios for a cable television (CATV) system. The modified spectrum analyzer is triggered for single sweep during the vertical interval of a selected channel, and the noise amplitude, peak sync tip amplitude and frequency of the channel are determined. The carrier-to-noise ratio is determined from the noise amplitude and the peak sync tip amplitude and the ratio and frequency are displayed. For triple beat ratio measurements a headend unit coupled between a television signal source and a combiner in the CATV headend prior to distribution offsets a selected channel by a predetermined frequency for a specified number of lines in the vertical interval. The modified spectrum analyzer measures the peak sync tip amplitude and a triple beat amplitude at the end of the specified number of lines.

Abstract: An improved swept frequency domain reflectometry instrument has an input/output terminal coupled to one end of a cable. A radio frequency at the input/output terminal is converted to an intermediate frequency using a swept local frequency. The radio frequency is derived from the swept local frequency and a variable offset frequency. A controller controls the variable offset frequency, monitoring the amplitude of the intermediate frequency. A period counter counts the intermediate frequency at a first maximum response of the intermediate frequency and further counts the offset frequency at a second maximum response of the intermediate frequency. The location of a discontinuity in the cable is calculated from the counted frequencies.

Abstract: An infinite dynamic range phase detector compares a test signal with a phase shifted reference signal which tracks the phase drift of the test signal. The incremental phase error between the test signal and the phase shifted reference signal is accumulated to provide an n*modulo(360) plus the increment between zero and 360 degrees output. A portion of the accumulated output is fed back as an offset which is applied to a reference signal to produce the phase shifted reference signal.

Abstract: An L+R separation system separates the L+R component of a composite stereo signal, such as a BTSC signal or an FM broadcast stereo signal, from the L-R suppressed subcarrier component by sampling the composite stereo signal at a rate which is twice the frequency of the L-R component subcarrier frequency. The sampling signal, which is derived from the composite stereo signal, is synchronized with the subcarrier frequency such that the sampling occurs at the zero crossings of the subcarrier frequency, eliminating the L-R component from the sampled output. A simple lowpass filter recovers the L+R component.

Abstract: An apparatus and method for expanding the resolution of digital-to-analog converters is described. Two limited resolution digital-to-analog converters are cascaded in such a manner that one converts the low order bits of digital input signal and the other converts the higher order bits. The output of the higher order digital-to-analog converter is applied directly to a summing circuit while the output of the low order digital-to-analog is first passed through an attenuator. When the low order digital-to-analog converter receives all logical ones, a carry is performed to the higher order digital-to-analog converter. The low order analog-to-digital converter is then reset by a successive approximation technique. Operation is essentially the same for borrow operation.

Abstract: A bi-directional data transmission and control system utilizing a central processing unit and a multiplicity of remote subscribers. Each subscriber is provided with a terminal coupled with the central processing unit by a suitable medium such as a CATV channel. Each terminal is provided with a demarcation plane separating common circuitry from a number of specialty modules and a common bus therebetween for circuitry simplification, application expandability and individual tailoring. The data transmission scheme efficiently utilizes the frequency spectrum and enhances polling frequency by permitting selective polling of any given specialty module or subscriber at any given time and by permitting simultaneous polling of every subscriber for service calls, thereafter locating the caller with minimal polling. Data transmission protocol is expandable or contractable for each terminal independently of others and permits data transmission between any two points in the system.