Abstract: Circuitry for detecting errors in a digital bit stream comprising a succession of data blocks and wherein each data block incorporates a parity check. At an error monitoring location, a bistable device toggles in response to either a logical "1" or "0" in the bit stream. The output of the bistable device is sampled at a submultiple of the bit rate and compared with a predetermined criterion to detect bit errors.

Abstract: Bidirectional communications between an alarm loop, comprising one or more alarm transmitters, and a remote receiver is provided through a digital transmission facility by a pair of interface units (201,301). Each interface unit, disposed at an end of the digital transmission facilities, provides encoding and decoding of signals to and from the alarm receiver. For greater reliability, each interface unit (601,701) can be adapted to select signals received from different digital transmission facilities.

Abstract: A technique for maintaining frame synchronization in a OAM system transmitting nondifferentially encoded data is disclosed. In accordance with the present invention, multibit words (F.sub.I, F.sub.Q) comprising framing bits are formed and inserted into the transmitter data channels. The value of the framing bit is insensitive to the rotational effects of phase ambiguity by having a predetermined value and by being inserted within a predetermined bit position in each data channel. In the disclosed embodiments, regeneration errors can also be corrected by the transmission of predetermined quadrant bits within the multibit words. In addition, the spectral tones generated by multibit word transmission can be reduced by the use of utility bits in the multibit words.

Abstract: A dual mode encoding/decoding technique for use in digital systems wherein transmitted digital words are limited, on average, to an alotted number of bits. The transmitted digital words are coded into first and second modes. The first coding mode utilizes predictive differential coding to provide a precision which can be greater than that obtainable by coding information solely with the allotted number of bits, while the second mode assures at least a minimum precision for the allotted number of bits. The first coding mode is transmitted as long as a preselected precision is provided. If not, the second coding mode is transmitted. In the disclosed embodiment, the dual mode encoding/decoding technique is applied to the transmission of color video signals.

Abstract: The linear distortion canceller circuit (104, 104-1) obliterates the linear component of any amplitude and/or group delay distortion in a double-sideband, amplitude modulated carrier signal. Pursuant to the present invention, the carrier signal is split into first and second signals. The first signal is multiplied by a mixing signal at twice the carrier signal frequency and the mixed first signal is then added with the second signal. The disclosed apparatus and method can be used in a communications system utilizing QAM modulation.

Abstract: The battery feed circuit (FIG. 3) provides a balanced dc feed current (I.sub.TR) to a 2-wire telecommunications path. The dc current in each conductor is generated by a bidirectional current source (103 or 104) which is responsive to one of a complementary pair of first control signals (S.sub.1, S.sub.1) along with a second control signal (S.sub.2). The complementary pair of first control signals is generated by a feedback circuit (105) which monitors the differential mode voltage (V.sub.TR) across the path. To reduce power consumption, the complementary pair of first control signals is a nonlinear function of the differential mode voltage. The resulting battery feed profile (FIG. 2) reduces the current on short path lengths. Longitudinal balance is provided by the second control signal which varies the currents generated by each bidirectional current source by equal amounts. This second control signal is generated by a second feedback circuit (109) which monitors the common mode voltage across the path.

Abstract: Automatic apparatus for precisely aligning first and second optical fibers (11, 13) end to end. The first optical fiber is coupled to an optical source (12). An end face (15) of the second fiber abuts an end face (14) of the first fiber. Detector apparatus (16-19 or 51) affixed to the circumference of the second fiber monitors the light transmitted in the cladding of the second fiber and generates a corresponding electrical signal therefrom. This signal is fed to electronic circuitry (27, 28, 7, 8, 31, 32 or 52, 61, 63, 64, 66, 67) which selectively activates fiber moving transducers (41, 42 or 69, 70 or 81, 82) to move the fiber end faces until the cladding light monitored is a minimum. This will maximize the transmitted light between the fiber cores. Once this optimum alignment is achieved, this position is maintained by the transducers.

Abstract: A new transmission system configuration is disclosed which takes advantage of the special properties of lightwave devices and the extensive availability of frequency space on optical fibers. The system employs a combination of time and frequency multiplexing at the transmitter, and frequency demultiplexing at the receiver. An advantageous result of combining time and frequency multiplexing is to relax the tolerance requirements on filters at the transmitter. A further advantage is to minimize the effects of mode dispersion introduced by the fiber.

Abstract: A carrier recovery circuit is disclosed for use in the receiver of a digital transmission wherein channels of data are formed by demodulating incoming quadrature-related carriers using receiver-generated, quadrature-related carriers. Phase alignment of the receiver-generated carriers to the incoming carriers is provided by integrated data from a preselected channel when the channels of data correspond to preselected regions in the signal space diagram.

Abstract: The adaptive threshold circuit (FIG. 1) senses the amplitude of a digital signal relative to a threshold and generates a corresponding output signal therefrom. Feedback circuitry generates a correction signal which drives the threshold toward a predetermined level in the signal-eye pattern. This predetermined level passes only through the region of intersymbol interferene in the signal-eye pattern.

Abstract: An optical receiver having enhanced dynamic range is achieved through the use of a variable impedance shunt 203 disposed at the receiver input. The optical receiver comprises an optical detector 102 serially connected to a transimpedance amplifier 201. The optical detector 102 receives an optical signal having a variable optical power level and modulation bandwidth and generates a corresponding electrical current therefrom. The transimpedance amplifier provides a fixed amount of gain and converts the electrical current to an output voltage. An automatic gain control circuit 202 produces a control signal which varies in response to the amplitude of the output voltage. The control signal is applied to the variable impedance device to vary the impedance therein. This maintains the output voltage at a predetermined amplitude over the modulation bandwidth without any significant reduction in receiver sensitivity.

Abstract: The fade character of a transmitted radio signal comprising an amplitude or phase modulated double-sideband signal is determined from the algebraic sign of the fade induced modulation and the location of the fade notch (.omega..sub.f) relative to the center (.omega..sub.c) of the double-sideband signal frequency spectrum. In the disclosed embodiment, the algebraic sign of the fade induced modulation is determined (e.g., 402, 403, 404, 405, 406, 409, 410, 411, 412, 413, 417) from the sign of the dc component of the product of the differentiated amplitude modulation and frequency modulation of the received signal. The relative location of the fade notch is determined by comparing the amplitudes (e.g., 402, 404, 405, 406, 415) of corresponding frequency components in each sideband of the received double-sideband signal.

Abstract: Switching between optical fibers is achieved through the use of a fixed (101) and a moveable (102) housing disposed within a slotted support member (103, 205). The fixed and moveable housings respectively contain first (104, 105) and second (108) sets of optical fibers. Each housing has two grooved (204) and parallel exterior surfaces. Both housings are disposed in substantial abutment to one another in the slotted support member with both sets of optical fibers parallel to one another. The sidewalls of the slot are grooved to be the mating opposite of the grooved housing surfaces. The first housing is fixedly positioned in the slot by the mutual engagement of the grooved exterior housing surfaces and the grooved sidewalls. Switching between optical fibers is accomplished by the translation of the moveable housing surfaces to either of two positions which axially aligns a predetermined number of optical fibers in the first and second sets.

Abstract: The fade character of a received double-sideband, phase coherent signal is determined from the location of the fade notch frequency, (.omega..sub.F) relative to the center (.omega..sub.c) of the received signal frequency spectrum and the phase between fundamental components of first (P.sub.1) and second (P.sub.2) product signals. These product signals are derived (401, 403, 411, 413, 419, 420, 421 or 801, 802, 803, 805, 811) using first (.omega..sub.1) and second (.omega..sub.2) spectral components that are symmetrically disposed about the center of the received signal frequency spectrum. The fundamental components of each product signal are at a common frequency.

Abstract: An improved fuse cap (11) which grasps an end of an elongated fuse (13) and mates with a fuse block (12) is disclosed. The fuse cap comprises a spring-loaded electrical terminal structure (32) which can be readily assembled into the fuse cap housing (31). The terminal structure serially connects the fuse element between the terminals (24,28) in the fuse block and provides connection to an alarm terminal (25) in the block when the fuse overloads.

Abstract: An improvement in tracking the signal-eyes (FIG. 4) formed by a digital signal is disclosed. This improvement is achieved by forming a sample at a regeneration sampling time (e.g., 404), a first sampling time (e.g., 401) and a second sampling time (e.g., 402). The first and second sampling times respectively precede and succeed the signal-eyes while each regeneration sampling time occurs within the signal-eyes. The amplitude of each sample represents the amplitude of the digital signal at the sampling time relative to a reference level (e.g., 301, 302 or 303) which passes through one of the signal-eyes. A first comparison signal is generated by comparing the amplitudes of the samples at the regeneration and adjacent first sampling times. Similarly, a second comparison signal is generated by comparing the amplitudes of the samples at the regeneration and adjacent second sampling times. The difference between the first and second comparison signal is then averaged to form an error signal.

Abstract: Sharp bends or kinks which produce microcracks in optical fiber cables are eliminated through the use of a strain relief assembly. The assembly comprises a straight cable duct (101) and a curved cable duct (102). The curved cable duct extends from the straight cable duct and guides an optical cable in a gradually curving path which lies in two orthogonal planes. This assembly is especially suitable for guiding optical cables to closely spaced circuit modules within an equipment bay or shelf.

Abstract: In a stripline transmission assembly, precise positioning of the metallic conductor (10) within the grounded channel (11) is achieved through the use of one or more support posts (20). Each post is inserted into a hole (30) in the channel bottom and extends through a hole (31) in the metallic conductor.

Abstract: Multifrequency (FIGS. 2 and 4) signals are generated by employing a microcomputer system (500) in conjunction with a digital-to-analog converter (506) and filter (507). Digital representations of amplitude values of the signals to be generated are stored in a read only memory (ROM 503) and sampled at a predetermined rate under control of a central processor unit (CPU 502) to generate digital signals representative of the desired multifrequency signal. The sampling rate is selected to be less than the theoretical Nyquist rate for the highest frequency tone in the multifrequency signal to turn to account the resulting so-called "alias" signals for generating tones closely spaced in frequency. In a specific example, the sampling rate is equal to twice the average frequency of the tones in the desired multifrequency signal. Unwanted harmonic components (3.omega..sub.0, etc.

Abstract: A smooth pulse sequence (SSM) which is a rational fraction (M/N) of an available uniform sequence (SIN) is generated by employing an address generator (10) and a read only memory (ROM 15). Signal representations are stored in the ROM (15) which define the smooth sequence pulse transitions. The address generator (10) is driven by the reference signal and, in turn, generates a sequence of address signals which, when applied to the ROM (15) cause the smooth pulse sequence (SSM) to be read out. The smooth pulse sequence (SSM) is filtered (16) and shaped (17) to obtain a desired uniform pulse sequence (SOUT) which is in synchronism with the reference signal (SIN).