Patent GB-485924-A (GB)
Title: Improvements in electrical systems
IPC: H04N5/06
Filed: 1936-11-23
Abstract: 485,924. Television. PHILCO RADIO & TELEVISION CORPORATION. Nov. 23, 1936, No. 32020. Convention date, Nov. 23, 1935. [Classes 40 (iii) and 40 (v)] A synchronizing signal of adjustable duration is derived from a source and is timed by a second derived signal. Current from the mains is smoothed in a tuned buffer valve in a unit 1, which also comprises a valve with a push-pull output, Fig. 5 (not shown). One phase of the output is applied to a unit 2a, which comprises two valves in cascade, which flatten the tops of the wave by grid-current effect to give a square-wave form, Fig. 6 (not shown). An harmonic is selected by tuned valves with inter-valve reaction and is shaped to a square-wave form in a unit 3, Fig. 8 (not shown). An harmonic of the intermediate frequency is selected by a unit 4, and is applied to a unit 5, shown in detail in Fig. 17 (Cancelled), which comprises a frequency halver and smoother. Synchronizing signals for horizontal scanning are obtained from one phase of the output from 5, which also supplies signals to a unit 6, shown in detail in Fig. 9, to form signals for blanking the ray on the return stroke. A sinusoidal signal is obtained by tuned amplifiers 66, 67 with a push-pull output circuit 68 and applied through phase-shifting networks 69, 70 to amplitude limiters 71, 72, to form square waves. These are combined in a limiter which passes current only where the two waves overlap for a duration determined by the networks 69, 70, as described in Specification 485,989. The output of opposite polarity from the unit 5 energizes a serrating unit 8 for the vertical synchronizing signal. The bi-phase signals from the unit 1 are applied to limiting-va,lves 36, 38, Fig. 7, of the unit 2b through a phaseshifting network 37 to produce a narrow pulse of adjustable duration as described above in connection with Fig. 9. The precise timing of the impulse is obtained by the intermediate-frequency signal from the unit 3, which is applied to a valve 45 connected to a common load 44. The output is passed through an amplitude-limiter 46 so biassed that a signal passes only when the low-frequency pulse from valves 42, 43 occurs simultaneously with a cycle of the intermediate frequency, Fig. 2 (not shown). A unit 9, which forms vertical blanking signals, is energized by the units 1, 3. In this, sinusoidal waves from the unit 1 and partially squared waves from the unit 2b are squared and added to a square wave of intermediate frequency from the unit 3, Fig. 10 (not shown). These are passed through amplitude-limiters to give a pulse at the framing frequency, the duration and occurrence of which is controlled by the intermediate frequency. The Specification as open to inspection under Sect. 91 comprises also a detailed description of the unit 5, shown in detail in Fig. 17 (Cancelled). The serrator 8 is shown in Fig. 19 (Cancelled). Current pulses, generated by a controlled blocking-oscillator 61, discharge a condenser 54, which slowly charges through a resistance 53 during the quiescent period. An additional resistance 53a limits the discharge. The voltage across the condenser 54 triggers a second blocking oscillator 57 when it reaches the synchronizing level. This occurs at equal intervals despite irregularities in the pulses produced by the oscillator 52, Fig. 8 (Cancelled) (not shown). The output is applied to a limiting valve 60, which passes only the tops of the pulses to a blocking oscillator 61 oscillating at half the frequency of the preceding stage, Fig. 10 (Cancelled) (not shown). The output of the limiter 60 is taken across a resistance 62, in the cathode circuit to obtain proper phase relation, and a similar resistance 64 in a final limiter 63 gives signals in opposite phase to those across an anode resistance 65. The horizontal synchronizing signals are applied to tuned amplifiers 73, 75 which are connected by a pushpull output circuit 76 to square-wave shaping valves 77 . . 80. The two cathodes of the two stages have a common biassing resistance and filter condenser so that, owing to the coupling condenser, the part of the negative cycle cut off by the second valve is different from the part of the positive cycle cut off by the first valve. When the outputs of the two branches are added by a common load resistance 81, narrow pulses of twice the input frequency are produced with a duration determined by the difference between the positive and negative portions, Fig. 6 (Cancelled) (not shown). The vertical synchronizing pulse from a unit 2b is added by a valve 82 to produce the wave 83, which is passed through a limiter 84 to cut off the portion below the dotted line. D.C. retention. An additional photo-electric cell at the transmitter is illuminated by the whole picture and supplies a current which is combined with the picture and synchronizing signals to maintain the datum level between them, Figs. 27 (Cancelled) and 28 (not shown). An amplifier for both A.C. and D.C. components is shown in Fig. 31 (Cancelled). At high frequencies the signal is transferred through a condenser C2 and the capacity to earth Cg of a battery B1 is isolated by resistances Z1, Z2. The unidirectional component is transferred through the resistances and battery which biasses correctly the grid of the valve V3. The transmitting line from the studio is coupled to the amplifier at the transmitter by a valve, which is coupled by a blocking battery, Fig. 35 (Cancelled) (not shown) or a cathode input circuit, Fig. 36 (Cancelled) (not shown). Owing to the low impedance of the line, no degeneration of the high frequencies occurs. The modulating stage includes two valves in push-pull, Fig. 37 (Cancelled) (not shown). The subject - matter of Specifications 485,990 and 485,991 also is included. This subject-matter does not appear in the Specification as accepted.