Abstract: A circuit for providing saw-tooth current, with a trace and a retrace interval, in a coil, in particular a deflection coil of a television kinescope, in which the coil is connected to a retrace condenser and a trace condenser so as to form a deflection circuit which oscillates freely during the retrace interval, is described. In this circuit, a first diode is connected parallel to the deflection circuit with such polarity as to be made conductive by the saw-tooth current during the first part of the trace interval, and the said deflection circuit is also connected parallel, by means of a second diode having such polarity as to be made conductive by the saw-tooth current during a second part of the trace interval, to a controllable switch, which is made conductive during part of the trace interval.

Abstract: A D.C. supply circuit for a television receiver which has a load circuit including at least one controllable semiconductor switch, the supply circuit comprising means for rectifying an alternating mains supply, a smoothing circuit connected between the rectifying means and load circuit and delay means for delaying the application of the full rectified and smoothed voltage to the load circuit when the receiver is initially turned on, wherein the delay means include means for inhibiting a certain number of cycles of the rectified A.C. voltage from being applied to the said smoothing means, so as to provide a D.C. voltage in which the number of cycles inhibited from reaching the smoothing means determines the delay with which the said D.C. voltage reaches the full value at the load circuit.

Abstract: The invention relates to broadcast receivers having a voltage controlled tuning device and in particular to a circuit arrangement for applying a voltage to the tuning device. The circuit arrangement is so designed as to be capable of producing tuning voltages to tune the receiver into the desired channels but at the same time being inhibited from producing voltages which tune the receiver into undesired channels such as police channels.

Abstract: The invention is concerned with a circuit arrangement for driving a saw-tooth current in a coil primarily intended for use as a line output stage for a television receiver. The circuit arrangement comprises a parallel resonant circuit which incorporates a line deflection coil, a diode connected in parallel with the coil to conduct the deflection current during a first portion of each operating cycle, a second diode and a thyristor connected in series with one another in parallel with the coil, the thyristor being fired by pilot pulses to conduct the deflection current in a second portion of each cycle immediately following the first portion, a series resonant circuit including a capacitor connected in parallel with a thyristor for quenching the thyristor at the end of the second portion of each cycle and a third diode connected in series with the capacitor in a circuit branch connected in parallel with the second diode and serving to transfer energy from the series resonant to the parallel resonant circuit.

Abstract: A circuit for providing saw-tooth current with a trace and retrace interval in a coil, in particular a deflection coil of a television kinescope, in which the coil is connected to a trace and retrace condenser with which it forms a resonant circuit, is described. In this circuit, a first diode is connected in parallel to the resonant circuit with such polarity that it is made conductive by the saw-tooth current during the first part of the trace interval, and the resonant circuit is also connected, through a second diode, to a controllable switch, which is made conductive at least during that last part of the trace interval, the second diode being connected with such polarity that it is made conductive by the saw-tooth current during the last part of the trace interval.

Abstract: A line output stage comprising a first parallel resonant circuit including a horizontal deflection coil and a capacitor, one side of the first resonant circuit being connected to ground and the other side of the first resonant circuit being returned to ground by way of a first diode and a controllable semi-conductor switch, a second diode connected in parallel with the first resonant circuit, a second parallel resonant circuit comprising a second coil having one side connected to a DC power supply terminal and the other side returned to ground by way of the controllable semi-conductor switch, means for applying periodic pilot pulses to the controllable semi-conductor switch and an energy transfer circuit inductively or capacitatively coupled to the said second parallel resonant circuit for transferring energy during each cycle from the second parallel resonant circuit to the first parallel resonant circuit, the said energy transfer circuit including a third diode and means for modulating the power transferred

Abstract: An image display device comprising a plurality of elements which can be made luminous is described. The elements are arranged in a matrix formed by rows and columns, and each column of the matrix is piloted by as many outputs of a delay line of the charge displacement type, fed by a video signal representative, for lines, of the image to be reproduced and by a clock signal. The main feature of the device is that the delay of the line is substantially equal to the effective duration of information in one line of the video signal, and that there are provided means for interrupting the passage of the clock signal to the delay line during a substantial period of time within the line blanking interval of the video signal, so that during the said period the status of the charges in the delay line remains unchanged, and said status is utilized to render luminous a row of the elements.

Abstract: A circuit for providing a saw-tooth current in a coil is described. The circuit comprises a trace condenser and a retrace condenser which form together with the coil a resonant circuit during the retrace interval, a diode connected parallel to the retrace condenser, a controllable switch connected to a supply source through an inductor and to the retrace condenser through a second diode.The main feature of this circuit is to comprise a condenser connected on one hand towards the controllable switch and the first inductor and, on the other hand, to a circuit comprising a second inductor and, through a third diode, towards the retrace condenser. The condenser and the two inductors are sized in such a manner that when the controllable switch is not conductive, energy is supplied to the condenser and that successively, when the controllable switch is conductive, the condenser is completely discharged through the second inductor. The energy thus stored in the second inductor is then supplied to a storage device.

Abstract: A television or radio receiver having electronic means for selecting the frequency to which the receiver is to be tuned, in which the selection is effected by means of a voltage controlled oscillator controlled by a control loop which receives the output signal from the oscillator, divides it by a number derived from a memory which stores a plurality of numbers corresponding to the available frequencies for reception by the receiver, compares the divided signal with a reference frequency to generate an error signal, and feeds the error signal through a low pass filter back to the control input of the amplifier. The time constant of the filter can be changed by short circuiting a resistor of the filter so that the control loop operates with a short time constant when actually selecting a frequency whereas it operates with a longer time constant while maintaining a selected frequency.

Abstract: A circuit for generating a saw-tooth current waveform in a coil comprises a parallel resonant circuit, of which the coil in which the saw-tooth current is to be generated forms part. The parallel resonant circuit includes two capacitors in parallel and a first diode, in parallel with one of the capacitors, and in parallel with which is a switching transistor connected via a second diode to the cathode of the first diode. Input energy from a power source is fed to the junction between the second diode and the switching transistor via an inductance which forms a resonant circuit with a further capacitor forming at least part of a reactance in parallel with the second diode.

Abstract: A color television system, such as the NTSC system, in which at least a part of the chromatic information is transmitted as suppressed carrier amplitude modulation of a subcarrier, and a subcarrier burst is inserted in the signal as a reference signal for use in demodulating the signal in which the subcarrier bursts are suppressed from some of the lines of the T.V. signal and replaced by signals carrying additional sound or picture information such as emergency messages, newsflashes or the like.

Abstract: A circuit arrangement for obtaining a periodic sawtooth current in a coil, particularly in a deflection coil of a kinescope, is described. The circuit arrangement comprises a first, unidirectional conductivity device, disposed in parallel to a circuit branch comprising the deflection coil, and a second, controllable switching device, having a control electrode connected to a source of periodic pulses which render conductive the second device during a part of the period of the sawtooth. The main feature of the circuit arrangement is to comprise a resonant series circuit disposed in parallel to the second device; the second device and the resonant series circuit are connected to the deflection coil and to the first device at least through a third, unidirectional conductivity device.

Abstract: A device for controlling the convergence of the side beams of a color television picture tube having three in-line electron guns, comprising two sets of coils wound on an annular ferromagnetic support in a configuration which, when an electric current is passed through one of the sets of coils, generates a magnetic field which influences only one of the side beams causing it to deflect in one direction and when an electric current is passed through the other of the sets of coils, generates a magnetic field which influences only the other of the side beams also causing deflection thereof in the said one direction. Deflection of the two side beams in a direction orthogonal to the said one direction is achieved independently by two further sets of coils which generate magnetic fields individually influencing associated side beams to cause deflection thereof by an amount depending on the magnitude and direction of the currents flowing in the coils.

Abstract: A telescopic aerial for a radio or television receiver is constructed to facilitate automatic assembly and comprises a plurality of tubular aerial elements surrounding a central stem, the elements are slidable within one another and each has an enlarged lower end, which is housed within the next outermost element, and a radially inwardly directed lip at the upper end. Between each pair of adjacent elements is a freely slidable axially split spring sleeve which frictionally engages the two tubular elements to prevent them from slipping with respect to one another. The enlarged lower ends of the tubular elements are also formed with inwardly bent tabs to limit the inward movement of the next innermost element when the aerial is collapsed.

Abstract: An amplifier circuit suitable for use as a video amplifier in a color television circuit for driving the variable impedance load provided by a color television picture tube, in which the load impedance of the amplifier element of the circuit is also made variable. This is achieved, in one embodiment by using as the output stage of the amplifier two transistors with a complementary symmetrical configuration so that one is always substantially cut-off while the other conducts. In another embodiment a transistor in common collector configuration acts as the amplifier element and its emitter from which the output of the amplifier is taken is connected by a diode to the collector of a transistor which feeds the base of the common collector transistor.

Abstract: A circuit for generating a saw tooth waveform in a coil such as the deflection coil of a television picture tube, comprising a first circuit branch including a capacitor serving as an energy storing current source and a controllable rectifier, and a second circuit branch including another current source, a second controllable rectifier and a resonant circuit comprising two reactances, constituted by an inductance and a capacitor which are connected in circuit by the second controllable rectifier and act to draw current from the two sources away from the deflection coil when the second controllable rectifier is fired whereby to initiate the flyback portion of the saw tooth waveform.

Abstract: An amplifier circuit suitable for use as a video amplifier in a color television circuit for driving the variable impedance load provided by a color television picture tube, in which the load impedance of the amplifier element of the circuit is also made variable. This is achieved, in one embodiment by using as the output stage of the amplifier two transistors with a complementary symmetrical configuration so that one is always substantially cut-off while the other conducts. In another embodiment a transistor in common collector configuration acts as the amplifier element and its emitter from which the output of the amplifier is taken is connected by a diode to the collector of a transistor which feeds the base of the common collector transistor.

Abstract: In a color television system a first periodic signal having subcarrier frequency is inserted into an amplitude-modulated carrier during line blanking interval with constant amplitude and there is inserted periodically into the first signal, at least once in every field scan, a second signal having a different mean amplitude from the first and a constant amplitude, an amplitude comparison between the first and second signals being utilized in the receiver to correct differential gain distortion.

Abstract: A receiver for radio or television signals having a channel selection device for controlling the frequency of a local oscillator whereby to adjust this to mix with signals on different selected frequencies to produce an intermediate frequency signal for demodulation, in which the local oscillator is controlled by a variable impedance device the impedance of which is varied by an error signal produced by comparing a reference signal with a signal divided down from the output of the local oscillator. The dividers are programmable dividers which operate with different division factors in dependence on a control signal from a keyboard or other control device. The reference oscillator is an oscillator used for other purposes in the receiver, and the local oscillator frequencies are multiples of 0.5 MHz, the intermediate frequency being 38.75 MHz.

Abstract: A circuit arrangement for demodulating the chrominance signal portion of a color television signal in an apparatus for receiving at least said color television signal is described. The chrominance signal to be demodulated is of the type that is coded according to the ISA (Identify Suppressing Alternately) system, i.e. the chromatic information modulates in amplitude by carrier suppression a subcarrier along two axes in quadrature, one of the axes being switched 180.degree. each line, a single reference signal of constant phase being inserted only every second line and serving as a reference signal for the demodulation of said subcarrier and as an identification signal for the switching. According to the invention, an electronic gate is provided which opens during part of every second line scanning period to allow the passage of the single reference signal to a passive crystal filter.