Abstract: A connector for hermaphroditic coupling with a similar connector has a hermaphroditic end cap which mates with the end face of the connector body when the latter is not in use. To ensure that the end cap is correctly located immediately the connector is disconnected, it is hinged to the connector body and spring-loaded to bias it closed. When two connectors are connected together, their respective end caps mate automatically so that they too are kept clean. This is possible because each end cap can pivot to a position in which its end face is coplanar with that of the connector body. Various locking devices are disclosed for locking two connectors together and for locking the end cap closed.

Abstract: To compensate for variations in a laser's peak power output due to changes in slope efficiency, a feedback loop is provided to monitor light output and effect compensatory changes in the drive current. In the feedback loop, the light output is detected by a photodiode. The output of the photodiode is filtered by a bandpass filter. The mean power of the filtered signal is determined and compared with a reference to control the laser drive. The reference takes account of the relationship between the filtered signal power and the peak power in the frequency spectrum of the pseudo-random input signal. The use of this reduced-bandwidth signal allows a relatively cheap, low bandwidth photodiode to be used with a long-wavelength laser.

Abstract: A conference circuit has a plurality of ports for a corresponding plurality of conferees. Associated with the ports is a control circuit which determines whether a conferee is active, i.e. talking, or dormant, i.e. listening. The circuit applies gain to the "active" signals and attenuates the "dormant" signals. When a listener starts to talk, the circuit switches his port to the "active" mode. Difficulties arise in determining when a listener becomes active, due to noise and echo with the speech signal. They are mitigated by comparing the signal from the port with an echo signal estimate derived from the echo return loss for the transmission path associated with the port. The arrangement takes account of differing echo levels for different transmission paths.

Abstract: A card having an uninterrupted strip of magnetizable material affixed to the surface of a substrate can carry a machine readable code in the form of a magnetized pattern. By removing alternate magnetized segments, in a column of parallel rifts across the strip, the machines readable code becomes non-alterable, since a uniform, unidirectional magnetization of the remaining material restores the original code.

Abstract: An overvoltage protection device, especially for telephone equipment and the like, comprises two protectors connected directly in parallel. One protector, for example a back-to-back semiconductor diode, has a breakdown voltage below which it is a high impedance. Between the breakdown voltage and a failure voltage it has a lower impedance. Above the failure voltage it has negligible impedance. The other protector, for example a gas tube, has a range of operating voltages which extends from below the breakdown voltage of the diode, to a voltage between the breakdown voltage and the failure voltage of the diode. In operation the two protectors interact, the diode operating, for example, on faster surges and, in so doing, slowing the surge front so as to increase the likelihood that the gas tube will fire.

Abstract: A platform for a ladder having rungs includes a frame and a step structure. The frame is arranged to detachably attach to at least one of the rungs of the ladder. The step structure is hingeably mounted to the frame for providing a footrest. The step structure is sized to swing upwardly and allow a foothold between the step structure and the frame. This foothold is supported by an intermediate one of the rungs.

Abstract: A non-random network can connect a common peripheral device to one of a plurality of computers. Each of these computers has a request line for providing a request signal. The network has a plurality of switching devices, each coupled to the common peripheral device and to a corresponding one of the computers. Each of these switching devices is operable in response to a select signal being applied thereto to transfer data between its corresponding one of the computers and the common peripheral device. The network also has a scanner coupled to the plurality of switching devices for operating them in a predetermined order by sequentially applying to them the select signal. This scanner is operable to cease sequencing and to continue applying the select signal to said switching devices to switch a selected one of the computers in response to a persistence of the request signal from the selected one of the computers.

Abstract: A receptacle for receiving a plug includes a frame and an electrical connector mounted on the frame. A switch is electrically connected to the connector and can disconnect it. A manually operable interlock has an on and off position. This interlock is mounted on the frame for operating the switch to apply power to the connector after the securing of the plug into the connector. The interlock has a grasping device for grasping the plug on a rearward external surface of the plug. The grasping device prevents the removal of the plug in response to the interlock being placed in the on position.

Abstract: An adaptive differential pulse code modulation system (ADPCM), with adaptive prediction, has a transmitter, which substracts the output of its predictor from the original input signal and transmits a numeric representation of the quantized difference, and a receiver which reconstructs the original input signal by the reverse process. Mistracking, whereby the receiver fails to faithfully reproduce the original input signal because its pole-based predictor coefficients differ from those of the transmitter predictor, which can result from transmission errors when the original signal comprises two pure tones, is avoided by eliminating the dependence of the adaptation process upon the predictor output. This is achieved by deriving the coefficients using the difference signal but not the reconstructed signal.

Abstract: A decoder is provided for decoding variable word length (VWL) encoded serial data in which each non-zero word comprises a start bit and an end bit of one state and a number of intervening bits of a different state, the number of such bits representing the magnitude of the word. The decoder comprises a binary counter and means responsive to a start bit of an input word for clearing the counter; responsive to any intervening bits present to enable the counter to count such intervening bits; and responsive to an end bit of said variable word to output the contents of the counter as a parallel binary word.Where the number of intervening bits is one less than the actual magnitude the decoder may include means for adding one to the counter output.The decoder may also detect an additional bit in the input word, representing, for example, its polarity, and provide a corresponding bit in the fixed-length output word.

Abstract: In a microwave device, for example a microwave local oscillator with a harmonic mixer for feedback control, problems of coupling the mixer circuit to the R.F. cavity are overcome by providing a d.c. blocking capacitor of the mixer on a planar surface of a support extending across an aperture in one wall of the cavity. In preferred embodiments the capacitor is a planar device formed by a plurality of interdigitated fingers. These fingers are oriented to couple magnetically with the R.F. energy at the aperture in the cavity. The support conveniently comprises a printed circuit board having a ground plane on the same surface as the capacitor, which is located in a small opening in the ground plane. A second ground plane is provided on the opposite side of the printed circuit board, overlying the opening. The two ground planes are interconnected by plate-through-holes.

Abstract: A unit can transmit driving torque from an input (32; 100) to an output (20; 118) shaft in a given rotational sense. Load torque of the same rotational sense, at the output shaft (20; 118), can cause that shaft to freewheel. The unit has a rotor (34; 104) arranged to be driven by the input shaft (32; 100). Also included is a hub (54; 132) coupled to the output shaft (20; 118) to rotate therewith. The unit also has a thrust device (46; 138). This thrust device (46; 138) is threadably and coaxially mounted on the rotor (34; 104) for running on the rotor (34; 104) and engaging the hub (54; 132).

Abstract: A microwave cavity oscillator has a semiconductor device, for example a transistor for exciting the cavity to oscillate. The device is mounted upon a substrate which is itself mounted, conveniently soldered, upon a carrier which is releasably secured in a chamber adjacent the cavity. The carrier and substrate are mounted so that the device is coupled to the cavity via a hole extending therebetween and can be removed and installed as a sub-assembly to facilitate tuning and other adjustments in a test bed. In preferred embodiments one end of the carrier is located in spigot-and-socket fashion in a recess surrounding a hole communicating with the cavity. The other end of the carrier is urged by spring means to positively and accurately locate the carrier relative to the cavity. A part of the substrate extends through the hole and into the cavity. The transistor is mounted on the part within the hole and the part within the cavity serves as a capacitive coupling probe.

Abstract: An overvoltage protection device, for protecting communications equipment against hazardous voltages cue to lightning or power surges, comprises a primary protector, for example a gas tube device, and a back-up protector connected in parallel. The back-up protector includes a semiconductor pn junction, and is preferably a pair of diodes back-to-back. The back-up protector has a breakdown voltage slightly higher than that of the primary protector and is arranged to fail short-circuit once it has operated so as to provide an indication that the primary protector failed to operate.

Abstract: In an adaptive equalizer of the decision feedback type for reducing intersymbol interference in subscriber loops of a telephone system, the corrected digital signal is applied to means for detecting the occurrence in the signal of a zero state following a non-zero state. When that occurs, a correlator samples the signal during the "zero" bit period and applies the sample to an integrator. The integrator output varies the coefficients of the feedback signal applied to the input means for addition to the incoming digital signal to provide the corrected signal. The equalizer may have several stages, each for detecting a "zero" state in a different bit period following the original pulse. Also the circuitry may be duplicated for each polarity if the input signal is bipolar.

Abstract: In a microwave device, particularly a microwave local oscillator, frequency variations due to temperature changes are reduced by supporting the tuning element, for example a quartz or sapphire crystal, in the end of a tube of INVAR or other material having a low thermal coefficient of expansion. The tube projects into the cavity from a hole in one wall thereof. Preferably the tube is positively located relative to the cavity by means of an external lip on the tube abutting a shoulder formed by a reduced diameter part of the hold adjacent the cavity. The lip may be urged into positive contact with the shoulder by a spring washer acting between the end of the tube and the opposed end of a bush screwed into the hole.

Abstract: A filtering system for potable water has a stand and a basket-shaped filter for filtering potable water. The stand has an upper cantilevered branch with an opening sized to hold said filter. This filter is detachably mounted in the opening.

Abstract: Bilevel coding of color video signals, for example video teleconference or NTSC broadcast television signals, is used to reduce the required storage capacity or transmission channel bandwidth. Each multi-level or continuous tone picture element in a frame is compared to a threshold and assigned one of two values depending upon whether or not it exceeds the threshold value. The threshold is produced by averaging the luminance components of neighboring picture elements and constraining the average by a signal derived from the chrominance of the original video signal. A significant feature is that the use of the chrominance signal in this way obviates the need, common to known monochrome systems, of adding noise (or dither signal) to the signal with concomitant picture degrading artifacts.

Abstract: A safety device allows controlled descent along a suspended rope. The safety device includes a base that rides the suspended rope. There is a manually operable apparatus mounted on the base which is used for adjustably gripping the rope. At least one handlebar is mounted transversely to the base, available for grasping by the escapee. In addition, a stirrup may be suspended from the base to provide further support for the descending escapee.