Abstract: A device for making discs, comprising a press which includes at least one hydraulic pressure chamber, one wall of which is formed during operation by a flexible, thermally conductive plate which can be pressed against a thermoplastic substrate. The device comprises a first system of ducts which includes a pump whereby a hot liquid can be supplied to and discharged from the pressure chamber, and a second system of ducts which includes a pump whereby cold liquid can be supplied to the pressure chamber. The liquid in the systems of ducts and the pressure chamber is pressurized by means of an expansion vessel, the liquid part of which communicates with the pressure chamber as well as with both systems of ducts, its gas part communicating with a pressure control device.

Abstract: An arrangement for centering, aligning and retaining a rigid disc such as a rapidly rotating video disc in an operating position, comprising a centering device mounted on a drive spindle, which device cooperates with a central disc hole in the disc, comprising a disc aligner mounted on the drive spindle for aligning the disc in a plane perpendicular to the axis of rotation of the drive spindle in the operating position of said disc, and comprising a disc loader for loading the disc towards the disc aligner. The disc aligner is rigidly connected to the drive spindle and the centering device comprises a plurality of resilient centering members which cooperate with the wall of the disc hole and which are radially movable between a rest position and an operating position which is situated nearer the axis of rotation of the drive spindle.

Abstract: Subscriber's circuit for connecting a subscriber's line to a telephone exchange, comprising a symmetrical amplifier which is arranged between two feed points having different potentials, the amplifier circuit having two input terminals and two output terminals, each one of the output terminals being connected to a wire of the subscriber's line and each input terminal of the symmetrical amplifier circuit being connected to an output of an associated digital-to-analog converter an input of which is connected to the one or to the other feed point by means of a change-over switch, the change-over switches being controlled in phase opposition by a binary digital signal which characterizes a voltage desired for the subscriber's line and which is derived from a digital signal generator under the control of the telephone exchange.

Abstract: A record carrier is described having an optically readable radiation-reflecting information structure, comprising information areas arranged in information tracks, which areas are spaced from each other by intermediate areas, the information areas having oblique walls. It is demonstrated that a suitable information signal and a suitable positional error signal are obtained if the angle of inclination of the walls of the information area lies between 65.degree. and 85.degree. and the phase depth of the information areas lies between 95.degree. and 140.degree..

Abstract: A facsimile circuit for a transmitter or a receiver, having an automatic switch-over between a photo and a text information signal processing. The more or less analog changing, photo information signal and the pulse-shaped changing, text information signal are converted into a binary signal suitable for supply to a reproduction device. A detection circuit, which performs a dual signal differentiation for detecting the presence of photo or text information controls a switch-over device through which the facsimile signal becomes available for transmission and/or reproduction after it has passed through an analog-binary or pulse-binary signal conversion circuit respectively.

Abstract: A multi-axial objective, comprising a number of adjacently arranged elementary systems which are formed by three spheres, the centers of which are situated on the same line, said systems being symmetrically arranged with respect to the center of the central sphere. The refractive index of the central sphere is larger than the refractive index of the outer spheres. The entrance and the exit of each system are adjoined by windows which form an entrance pupil and an exit pupil, the former being arranged in the center of the entrance sphere, while the latter is arranged in the center of the exit sphere. The windows are proportioned with respect to the diameter of the spheres so that the field of each system overlaps the field of the directly adjoining systems, the field image of the multi-axial objective being uniformly illuminated.

Abstract: Attenuation equalizer for correcting within a frequency range the temperature and frequency-depending attenuation variation of cables, comprising a cascade arrangement of a fixed and a variable attenuation correction circuit, connected to a control circuit, the variable attenuation correction circuit comprising a bridge-T network having a series arrangement, of two identical series resistors bridged by a variable bridging impedance and a parallel impedance connected between these two series resistors, the fixed attenuation correction circuit having a lower attenuation for higher frequencies than for lower frequencies, the temperature dependency of the cable being eliminated in the variable attenuation correction circuit and the frequency dependence being eliminated mainly in the fixed attenuation correction circuit for which purpose the variable attenuation correction circuit comprises only two adjustable components.

Abstract: Apparatus is described for removing stereophonic signals contained in a broadcast signal. Removal of a stereophonic indicator tone frequency on the broadcast signal is also provided. Separate outputs measuring both a summation signal of left plus right audio signals and a difference signal of left minus right audio signals are provided. Matrix means are also included for separating left audio signal and right audio signal from the summation and difference signals. These recovered audio signals may be monitored by standard broadcast instruments to observe the performance level of the broadcast signal.

Abstract: An optical read unit for reading radiation-reflecting video discs comprises a semiconductor laser which with the aid of a scan wobbler and a focussing wobbler is moved at high frequency in two directions relative to the video disc, a radial direction for tracking purposes and a direction normal to the disc for the purpose of automatic focussing. The semiconductor diode laser is mounted on a metal radiation source carrier which is connected to a heat sink for carrying off the heat with a low temperature gradient, and is driven by piezo-electric plates.

Abstract: Two time division multiplex switches connected to the ends of a time-division multiplex bus are controlled so that they are closed during a periodically repeated time interval. Connected to the terminals of each two-wire line circuit is a capacitor and a switch, which is synchronously controlled with the time-division multiplex switches so that during each time interval the capacitor is charged to a voltage present on the time-division multiplex bus and that during the successive time intervals the discharge time constant of the capacitor is so long that the voltage of the electrodes of the capacitor remains substantially constant. The voltage is connected across the impedance of the corresponding two-wire line circuit.

Abstract: The position of an optical or opto-electronic component, such as a lens or a plate provided with a number of light-sensitive semiconductor diodes, can be adjusted in two directions of adjustment which are perpendicular to each other with the aid of an appropriate adjusting device. The adjusting device comprises two bending hinges consisting of portions of a leaf spring, which bending hinges are perpendicular to each other, the one hinge being bent relative to a stationary frame to which the adjusting device is secured and the other bending spring being bent relative to the first bending spring. The two bending springs may consist of portions of a single unit manufactured from a suitable spring material.

Abstract: A recording and/or reproducing apparatus for a record carrier in the form of a tape, with a plurality of parallel longitudinal tracks. The apparatus comprises positioning means for controlling the position of the write/read head transverse to the direction of movement of the record carrier. The control signal for these positioning means is obtained with the aid of two optical systems, which each comprise a light-emitting element for emitting a radiation beam which is aimed at one edge of the record carrier and a light-receiving element for picking up the amount of light which shines past said record carrier, at least one of the elements of each optical system being rigidly connected to the write/read head. A detection device is coupled to the two light-receiving elements, which device derives the desired control signal from the amounts of light received by these two light-receiving elements.

Abstract: A ringing signal generator for generating a ringing current in a subscriber's line uses a line current inverter controlled by means of a pulse code modulated signal obtained by encoding a sinusoidal ringing signal by means of a delta modulator at a sampling frequency which considerably exceeds the frequency of the ringing current.

Abstract: An electronic transmitter for direct current telegraphy by means of polar line currents has a switching circuit that selectively connects one of the two poles of a telegraphy battery through a unipolar constant current source to a telegraph line, and an output filter having a capacitor in parallel with the telegraph line. The higher frequencies in the telegraphy signals are sufficiently suppressed to keep the noise level in adjacent telephone lines below a prescribed value because the output filter also has two complementary branches in parallel with the telegraph line, at least one of the two branches supplying, in response to a polarity transition of the line current supplied by the current source, a correction pulse having a polarity opposite to the line current to the telegraph line. This output filter is assembled from small-sized, low-priced elements so that an efficient miniaturization of the electronic transmitter in its entirety can be realized.

Abstract: A system for signalling the fact that the fuses and limiting diodes in the connecting circuits of telephone lines are defective. Use is made of the rest supply resistors already present in the connecting circuits and the loop detector which is normally used for detecting calls. The fuses and limiting diodes are connected in such a way that a defect causes the loop detector, which is constructed as a differential voltage detector, to signal a call.

Abstract: Apparatus for reading a record carrier provided with a spiral structure in which sound and/or image information is stored in the form of frequency modulated or phase modulated signals is disclosed. The carrier structure is composed of coplanar regions of variable length separated by coplanar areas of variable length. Where the regions and areas are all in the same plane the regions and areas have different coefficients of reflection or transmission. Where the regions and areas are not coplanar they are spaced by a distance sufficient to produce in response to impinging radiation a one-half wave length difference in the radiation exiting the regions and areas. The apparatus provides a light beam with a frequency that facilitates diffraction of the beam by the areas and regions, and also provides a radiation sensitive detection system for converting the light beam modulations caused by the record carrier into a corresponding electrical signal.

Abstract: The invention relates to a method of eliminating errors in images of patterns which consist of periodically arranged individual images by optical filtering, only certain selected diffraction orders of the regular pattern to be imaged in the form of a ring or parts of a ring being employed for further imaging.

Abstract: A video disc player is provided with a stabilizing disc which during playing is disposed at a small distance above the video disc, air being admissible through an inlet restriction between the stabilizing disc and the video disc so that locally a sub-atmospheric pressure is produced as a result of the centrifugal pumping action of the video disc. In order to prevent the video disc from being drawn along when the stabilizing disc is moved upwards, an air by-pass passage is provided which via air-valve means can be opened when playing of the video disc is terminated, so as to admit an increased air stream between the stabilizing disc and the rotating video disc in order to at least substantially eliminate the prevailing sub-atmospheric pressure.

Abstract: Interference insensitive line supervision circuit for subscriber's line having a given working range for the line potentials. A call can be simulated by the occurrence of overvoltages. Means are applied which supervise the occurrence of overvoltages. In the case of overvoltages these means produce control signals which result in that the state of a line state store cannot be affected by the line supervision circuit.

Abstract: A completely automatic suppression of an echo in a video signal is accomplished by using a multiplying circuit in the amplitude and polarity control of a correction signal which must compensate for the echo and an automatic control of the time delay of the correction signal by means of an echo polarity correction switch with which the polarity of the setting of the delay control characteristic is matched to the polarity of the echo to be suppressed.