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: 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: 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.