Abstract: A playback apparatus, in particular a video player, for playing back round disks, which are provided with information tracks which are optically readable with the aid of a read beam obtained from a light source, and having a housing which comprises a substantially flat covering plate and an optical focussing device movable to and fro in a slot in the covering plate. In view of the safety of the apparatus and for other, such as aesthetical, reasons the slot is closed by a closing element in every position of the focussing device, which element is connected to the focussing device and for example consists of a flexible strip of a width greater than the width of the slot.

Abstract: An apparatus is described for reading a record carrier on which information is stored in an optically readable structure. Between a radiation source and an objective system a mirror system is disposed, by means of which the entrance pupil of the objective lens can be imaged onto beam-controlling elements which deflect the read beam over the information structure.

Abstract: A circuit arrangement for a tone push-button selection telephone subscriber set, in which a tone signal generator and a microphone amplifier are coupled to direct current networks, each of which is coupled to an output network such that two current mirror circuits having the same current ratio factor are obtained. The direct currents in the networks are exclusively switched by means of a long-tailed pair, so that the direct current flowing in the output network has a constant value.

Abstract: The invention relates to a deflection prism arrangement for the formation of a dot pattern for digital electro-optical light deflectors, e.g. laser light deflectors, in which the prism angle of each of the sequence of prisms is doubled, the prism apex angle of the double-refracting prisms with larger prism angles being intersected in such a way by the plane in which optic axis of the prism is disposed, which axis is perpendicular to the system axis, that the two partial angles formed with the optic axis of the relevant prism have a ratio between approximately 2/3 and 3/4.

Abstract: An arrangement for focussing an image of an information structure which is disposed on or in a substantially flat record carrier, light being projected onto the light-sensitive detector via an optical element and a record carrier, which detector via a control system controls the optical element, the control system also receiving a signal which is a measure of the velocity of movement, which signal limits said velocity of movement.

Abstract: A circuit arrangement for generating an output frequency by division of an input frequency by adjustable divisors. Use is made of a first adjustable frequency divider having an output wherefrom the output frequency is derived, and a further frequency divider which is connected as an adjustable selection circuit and the counting input of which receives the output frequency. The input frequency is applied to the counting input of the first frequency divider via a gate. The output of the selection circuit is connected to one input of the gate such that each output signal of the selection circuit suppresses a given number of pulses of the input frequency.

Abstract: An opto-electronic photocoupling device in which the light emitter and receiver are coupled optically by a light conductor, and the conductor is constituted by a drop of a first transparent resin embedded in a second resin which is also transparent, the index of refraction of the first resin being higher than that of the second resin.

Abstract: An apparatus is described for reading a flat reflecting record carrier on which information is stored in an optically readable structure, which apparatus, inter alia, includes an objective system for focussing a read beam on the plane of the information structure and a focus detection system which is coupled to an electronic circuit for deriving a control signal for controlling the position of the objective system relative to the plane of the information structure. The electronic circuit is equipped so that the control signal ensures that during locking-in the objective system is moved with a low preferably constant, speed towards the record carrier until the required position is substantially attained, after which the objective system is subject to a high acceleration in the opposite direction.

Abstract: An electronic telephone subscriber set which is suitable for co-operation with a telephone exchange incorporating supply resistors, the values of which are substantially higher during the detection of the closed/non-closed conditions of a subscriber loop than during the speech condition and which is provided with an adjustable direct current resistor connected across the line connection terminals and a current detector coupled thereto for adjusting the direct current resistor to one of two values in dependence of the line current in order to enable optimum detection of the closed/non-closed conditions of the subscriber loop.

Abstract: A device is described for determining the linear displacement of a machine tool component with the aid of a grating which is mechanically connected to the component, which grating is disposed in the light path between a light source and a light-sensitive element which converts the incident light into an electric signal. The light-sensitive element is a multiple photo-cell which consists of a row of line-shaped photo-diodes which by means of an electrical switch are consecutively connected to an electronic circuit which processes the signal which is produced in the photo-diodes.

Abstract: An arrangement for digitally processing a given number of analog channel signals, more particularly a digital multiplexer and demultiplexer provided with a number of signal paths each comprising a recursive digital filter and delay circuits arranged in cascade therewith, said filter circuits having an amplitude-frequency characteristic of a lowpass filter having a cut-off frequency which is equal to half the bandwidth of a channel signal and a phase-frequency characteristic which is such that the difference between such a phase-frequency characteristic and the phase-frequency characteristic of a reference digital filter has a sawtooth-shaped variation, the slope of the sawtooth being opposite to the slope of the cooperating delay circuit. The arrangement furthermore comprises in cascade a discrete Fourier transformer connected to the signal paths.

Abstract: In an opto-electronic focus detection system for determining a deviation between the plane of focussing of an objective and a radiation-reflecting surface the path of a focussing beam which is reflected by said surface includes an assembly of two radiation-sensitive detection elements. The difference in the output signals of said elements is proportional to said deviation. By disposing a lenslike element of which only the outer zone has a lens action before the detection elements, the measuring range can be extended while maintaining the sensitivity for small deviations.

Abstract: A device for the thermomagnetic recording of information on a highly coercive magnetizable recording medium. For this purpose is used, for example, a video recorder of the "helical scan" or "transversal scan" type whose drum has a co-rotating mirror and system of lenses with which an energy beam is directed and focussed on the recording medium at a small distance in front of the recording gap of the magnetic head. As a result of this the coercive force of the recording medium is locally reduced while using a very short heating time so that the medium can be recorded there by the head.

Abstract: A device for writing information in a disk-shaped record carrier, and/or for reproducing the recorded information, the transducer being radially movable relative to the record carrier, which transducer is disposed on a tubular member, which at its one end is provided with a drive coil and at its other end with a tachometer coil, which coils are movable in an air gap of a stationary magnet system.

Abstract: An apparatus is described for reading a record carrier on which information is stored in an optically readable structure. Between a radiation source and an objective system, a polarization-sensitive beam splitter and a .lambda./4 plate are disposed. The optic axis of the .lambda./4 plate is perpendicular to the end faces, so that the plate may be thick and may be rotated in its own plane.

Abstract: A method of image enhancement is described. A number of images of different unsharpness are separately filtered and subsequently combined. The various filters have complementary apertures.

Abstract: In an apparatus for reading a record carrier on which information is stored in an optically readable structure, the radiation which is supplied by the radiation source is split into a read beam and an auxiliary beam for determining the focussing of the read beam on the record carrier. Said auxiliary beam is intercepted by two radiation-sensitive detectors. By disposing a radiation-absorbing knife between the radiation source and the Wollaston prism a part of the auxiliary beam is blocked. Thus, an accurate indication can be obtained of the magnitude and the direction of a focussing error.

Abstract: In a record carrier for the storage of a television signal in an optically readable track-shaped structure, the information is contained in the frequency and/or amplitude of an undulation of the tracks of constant trackwidth. Via a phase-reading mechanism an electric signal can be obtained which is substantially linear with the television signal to be written. When transferring a television signal via such a record carrier the electric signals need not be limited abruptly. As a result, no higher harmonics occur, and substantially no mixing products occur in the frequency band of the luminance information and in the frequency band(s) of other information, for example chrominance and sound information.

Abstract: A transmission system for pulse signals of fixed clock frequency with regenerative repeaters located in the transmission path, each being provided with a pulse regenerator and a clock extraction circuit recovering the clock frequency for the control of the pulse regenerator from the received pulse signals with the aid of a frequency selective circuit. The use of a special type of frequency selective circuit results, especially in transmission systems having a large number of regenerative repeaters, in a considerable reduction of the phase jitter of the recovered clock signal in the receiver without detrimentally influencing the acquisition of the clock frequency in the individual regenerative repeaters.

Abstract: An arrangement for simultaneously producing signals having a decreasing frequency and signals having an increasing frequency. In this arrangement the signals have frequencies which are complementary relative to the double value of a central frequency. The arrangement includes a pair of voltage-controlled oscillators controlled by signals supplied by a control generator. The arrangement is characterized in that for each oscillator there is provided with a phase control loop and that the control generator is of the digital type designed to supply two pairs of digital signals. One pair is applied to the frequency dividers and the other is applied to the oscillators so as to tune them to such a frequency that they are in the operating range of the phase control loop.Use: Radio-electric transmission of data.