Abstract: In projection television apparatus in order to prevent burning of the phosphor screen of at least one of the television projection tubes a display is not produced should there be an interruption or substantial reduction in the deflection current through one of the line or field deflection coils. Each deflection coil is connected in series with sensing means for separately sensing the deflection current flowing therethrough. In the event of one of the currents through one of the deflection coils being interrupted or substantially reduced means responsive to said sensing means prevents picture information from being applied to the control grids of the projection tubes.

Abstract: A method of and arrangement for digitizing a video signal using a picture transform coding, wherein a group of N video signal samples is converted into a group of N coefficients y(m) wherein m=1, 2, 3, . . . N which are each adaptively encoded.In order to prevent a coefficient y(m) which is on average small to very small, from being insufficiently accurately encoded, or not encoded at all, when it is occasionally large, the group of coefficients is compared with a number of fixed classification groups A(j) each consisting of M elements a(j,m), wherein a(j+l,m).gtoreq.a(j,m) and j=1, 2, 3, . . . M. The j is determined in such manner that y(m)<a(j,m) for all m.A bit-assignment group B(j) having elements b(j,m) is associated with each classification group A(j) and each one of the N coefficients y(m) is now converted into a code word z(m) which contains a number of bits which is characterized by b(j,m) and which is, for example, equal to the value of b(j,m).

Abstract: Loudspeaking telephone set having a hand set connected thereto for soft speaking. When the hand set is placed on the telephone set, the microphone and the loudspeaker being in the switched-on condition, there is a risk that oscillations or singing will occur due to acoustic feedback. In order to avoid this risk, the hand set is provided with an ultrasonic transmitting device and the telephone set is provided with an ultrasonic receiving device 13. The receiving device comprises means to determine the propagation time of the ultrasonic signals and means for affecting the gain of the loudspeaking channel of the telephone set in dependence on the propagation time.

Abstract: A hook-type connection for the play-free connection of two parts. A first part comprises a hook with wings which engage an edge which is formed on an abutment on a second part. In the assembled condition, the wings are pivoted about the longitudinal axis of the shank of the hook, so that the hook is subjected to a torsional load. A hook-type connection of this kind offers optimum freedom of design for the different manufacturing tolerances of the parts and the hook-type connection occuring during practice.

Abstract: Circuit arrangement for generating a sawtooth voltage which has a substantially nominal frequency in the absence of synchronization pulses, whereby the changeover to direct synchronizability takes place as soon as a synchronization pulse comes into coincidence with the sawtooth flyback. In this way a phase change is avoided when the changeover is made. The changeover to nominal frequency occurs as soon as a pulse fails to occur within the natural period effective in case of direct synchronization. A threshold value circuit has an intermediate value which prevents synchronization by interference pulses occurring prematurely.

Abstract: Telephone subscriber's line interruption arrangement comprising a series arrangement of a semiconductor interrupter contact and a control circuit connected between a first line terminal and a second line terminal, in which a subscriber's line can be connected to the line terminals and via a hook contact. In order to ensure that at low line currents, that is to say in the case of long to very long subscriber's lines, the voltage drop across the interrupter contact is kept very low, the control circuit comprises an output circuit which ensures that the voltage at the control electrode of the semiconductor interrupter contact is at least equal to the voltage at the first terminal.

Abstract: Circuit for the delayed switch-on of a supply voltage in an electric apparatus which has at least a first and a second supply terminal, the series arrangement of the emitter-base path of a first transistor and the collector-emitter path of a second transistor being arranged between the first and the second supply terminals, the base of the second transistor being connected to a voltage divider provided between the collector of the first transistor and the second supply terminal.

Abstract: A telephone set comprising an input unit, a signal generating unit and an information processing unit, which may comprise a read-only memory, a microprocessor or a special LSI circuit for converting information supplied by the input unit into information to be transmitted. In order to obtain a greater reliability as a telephone set, a supervisory circuit, a switching unit and a d.c. isolated signal path have been provided between the switching unit and the information processing unit for coupling the input unit to the signal processing unit via the d.c. isolated signal path and for, possibly, coupling the signal processing unit to the signal generating unit when the supervisory circuit detects proper operation of the information processing unit and for connecting the input unit to the signal processing unit when the supervisory circuit detects a faulty operation of the said information processing unit.

Abstract: Voltage stabilizer for use in a telephone instrument, comprising the series arrangement of the main current paths of two transistors (4, 6) and a voltage divider (8, 9) connected in parallel therewith connected between first (1) and second (2) terminals. The bases of the transistors (3, 5) are connected to the voltage divider. The transistors (3, 5) and (4, 6) are connected in the Darlington pair configuration. In addition, in order to obtain a high AC impedance, the stabilizer includes a capacitor (11) which is arranged between the bases of transistors (3, 5) and terminal (2) to which the emitter of the second transistor (6) is coupled. To reduce the switch-on time of the stabilizer, a thyristor (13, 14) is provided between the first terminal (1) and the base of the first transistor (3) and a voltage divider (17, 18) whose tap (19) is connected to the cathode gate of the thyristor circuit is connected between the first terminal (1) and the junction of the main current paths of the transistors (4, 6).

Abstract: A circuit comprising a line interruption arrangement for producing dial pulses, comprising a series arrangement of a semiconductor switching element and a control device connected between a first and a second line terminal, the first and second terminals being provided to enable connection to a subscriber's line. To limit the current in the subscriber's line while using a minimum of components, the control circuit comprises a current detection device which is connected to the control electrode of the semiconductor switching element to drive the semiconductor switching element into saturation when the line current is below a predetermined value and to drive the semiconductor switching element out of saturation when the line current is above the said predetermined value.

Abstract: This arrangement comprises a controllable attenuation circuit of the voice signal received, a pulse-duration modulator which produces pulses the duration of which is modulated by the voice signal supplied by the controllable attenuation circuit, an overshoot detection circuit which produces from the modulated pulses a compression pulse each time it is detected that the amplitude of the modulated voice signal reaches a certain threshold, the compression signal produced by the said overshoot detection circuit being applied in the attenuation circuit to an integrating circuit which produces the attenuation control signal. The amplifier of the loudspeaker receives the modulated signal.

Abstract: A sawtooth voltage oscillator synchronizable by synchronizing pulses, a capacitor being charged and discharged, respectively, between two threshold values. The free-running frequency of the oscillator is switchable under the influence of a synchronizing signal detector which establishes the frequency of the synchronizing signal.

Abstract: A device which provides a video playback apparatus that plays a video disc having different video information and special purpose information tracks. A multi-line video information storage circuit, a special purpose information storage circuit and a radial tracking mirror are controlled by a timing circuit in such a manner that the special purpose information track is sampled for a predetermined period and stored video information is displayed such that continuous video information and special purpose information recorded on the video disc is presented contemporaneously to a monitoring means.

Abstract: To render a setting circuit more suited to the use of a microprocessor, the frequency of pulses applied by a setting shaft are periodically measured and the value found is multiplied by a weighting factor which depends on the speed of rotation of the setting shaft. The weighted, measured values are integrated and the integrated value can be used to tune a receiver or to set the time display of a clock.

Abstract: A DC supply for an electronic signalling device that is connected to a signal transmission line. The device comprises a plurality of circuit units each of which must be supplied with a DC-supply current. Feeding the circuit units in series has the advantage that the DC-supply current in each of the circuit units can be utilized to the full. A drawback is that the different supply voltages add up. A practical requirement may be that the total supply voltage does not exceed a certain value at a certain value of the supply current. In order to satisfy this requirement means are present which cause the supply voltage of one of the circuit units to decrease more than proportionally to the DC-supply current when the DC-supply current decreases to below a certain value.The invention is suitable for use in loud-speaking telephone sets.

Abstract: The circuit arrangement in accordance with the invention comprises an RC-element, to which the same direct voltage is applied as the amplifier. When the direct voltage is switched on or off the capacitor is either charged or discharged, the resulting oppositely directed voltages being applied to the anti-parallel base-emitter junctions of two transistors, whose collectors are interconnected. The collector voltage of these transistors serves to control a semiconductor switch included in the audio frequency branch.

Abstract: When electronic circuits are used for applying a conventional ringing voltage which has been superimposed on the conventional supply voltage, they require a high supply voltage. According to the invention an a.c. voltage is used in which that portion of each period in which the polarity is positive differs from the portion in which the polarity is negative. This a.c. voltage has a DC-component by means of which the condition of the subscriber's loop can be detected. The peak-peak value of the ringing voltage may be twice the maximum permissible voltage swing of a wire of the subscriber's line, which is an optimum.

Abstract: A low-pass transfer is effected between the two stages in an asymmetrically driven differential amplifier, which transfer has a negative effect on the high frequencies. The measure embodying the invention provides by means of a further transistor a negative feedback circuit which causes the low-pass filter to be of a low resistance or because of which it need only process low voltages. This greatly improves the transmission for high frequencies.

Abstract: A RF signal converter circuit for connection to the aerial input of an RF superheterodyne receiver. In order to avoid a separate remote control of the converter circuit use is made of the local oscillator radiation which is present at the aerial input of a RF-superheterodyne receiver as an indication of the tuning frequency selected by the user with tuning portion of the said RF superheterodyne receiver. The converter circuit comprises a frequency search circuit in which the frequency of the oscillator radiation is detected, an RF signal selector which is controlled by the frequency search circuit and by means of which the desired RF signal is selected from the RF signals applied to the converter circuit, furthermore comprising a modulator which is also controlled by the frequency search circuit and in which the selected RF signal is modulated on a carrier frequency which is determined by the tuning frequency and the intermediate frequency of the RF superheterodyne receiver.

Abstract: A variable-gain differential amplifier comprises a first long-tailed transistor pair between the bases of which the input signal is applied. The emitter-collector paths of the transistors of the first pair are included in the tails of second and third long-tailed transistor pairs respectively, and load resistors between the lower terminals of which the output signal appears are included in the respective collector circuits of one transistor of each of the second and third pairs, and hence in the collector circuits of the respective transistors of the first pair. The second and third pairs are controlled by a gain control signal thereby diverting a variable proportion of the collector signal currents of the transistors of the first pair away from the load resistors (17,18) and hence varying the gain of the circuit. In order that variations in the gain control signal should not affect the d.c.