Abstract: Dispersion is reduced in a graded index optical fiber having a finite number of core layers by introducing slow longitudinal variations into the index of refraction of each layer. The index of refraction of each layer varies between a maximum which is proximate in value to the minimum index of refraction of the more central radially adjacent layer and a minimum which is proximate in value to the maximum index of refraction of the next furthermost radially adjacent layer.

Abstract: The concentricity and uniformity of a plastic coating as it is applied to an optical fiber are monitored by comparing the backscattered light patterns generated by two mutually perpendicular light beams incident upon the coated fiber.

Abstract: A repeater monitoring and fault location system is disclosed for a submarine cable system which includes repeaters of the type having separate high band and low band amplifiers for two-way transmission over one cable. Each repeater includes an oscillator for generating a signal at a frequency in the cutapart region between the high frequency and low frequency transmission bands and which is uniquely identifiable to that repeater. A test tone at a frequency in the low frequency transmission band is transmitted from the low frequency transmitting end along the cable. The low band amplifiers intermodulate the local oscillator signals with the transmitted test tone to generate a series of seond order modulation products at frequencies in the high frequency band. A low pass filter, designed to have a controlled moderate level of loss in the portion of its high frequency stop band over which the frequencies of the second order modulation components lie, is connected to the output of each low band amplifier.

Abstract: A fault interior to an overmoded waveguide transmission line is located by pneumatically propelling an electrically semi-transparent reflecting piston within the waveguide line. The piston is designed to give low forward insertion loss yet at the same time a sufficient reflection in response to a transmitted millimeter wave test pulse stream. By measuring the magnitude of the signal reflected from the piston and returned to the transmitting terminal as the piston is moved along the waveguide length, the transmission loss of the waveguide is determined as a function of distance from the transmitting terminal. By examining the transmission loss measurements for any abnormal step or slope change or ripple which would be indicative of a waveguide fault, the location of a fault can be precisely determined.

Abstract: A frequency mixer-downconverter which can be tuned as either a single sideband mixer or a double sideband mixer and which has a wide tunable RF bandwidth and low conversion loss is disclosed. A high-frequency input signal is coupled from an input waveguide to a shielded suspended stripline. Two Schottky barrier diodes are connected proximate to the waveguide-to-stripline transition, between the inner conductor and the outer conducting channel of the stripline. The two diodes intermodulate the input signal with a subharmonic pumping signal which is also coupled to the suspended stripline from a waveguide input. An intermediate frequency signal, at a frequency equal to the difference between the input signal and twice the frequency of the pumping signal, is generated as an intermodulation product and transmitted on the suspended stripline to an output.

Abstract: Active and standby clock signals are phase synchronized to each other within a predetermined phase tolerance by synchronizing each clock signal to the same reference pulse stream. A first synchronizing pulse signal is derived from the active clock signal and a second synchronizing pulse signal is derived from the standby clock signal. For each synchronizing pulse signal, the pulse widths exceed the reference signal pulse widths by an amount related to the predetermined phase tolerance. Synchronization between the active and standby clock signals is achieved when the phases of the active and standby clock signals are adjusted such that the pulse widths of the reference pulses lie entirely within the time domain of the pulse widths of the synchronizing pulse signals.

Abstract: In a digital transmission system that encodes each sample of a video signal into a variable bit length data word to form a consecutive stream of variable bit length data words, synchronization between the received data words and their properly associated spatial addresses is maintained by periodically interposing synchronization words into the transmitted data stream. After initialization at the beginning of a video field, each picture element along each active scan line is consecutively sampled and encoded into a variable bit length data word. Each scan line is divided into segments having a predetermined number of sample positions included therein. A word counter cyclically counts each sample as it is encoded to provide a representation of the horizontal position of each code word within a segment along a scan line. The relative horizontal position of each code word is thus represented by the count of the word counter.