Patent GB-763193-A (GB)
Title: Improvements in or relating to wired television broadcasting systems
IPC: H04N7/10
Filed: 1952-12-12
Abstract: 763,193. Distributing music &c. BRITISH RELAY WIRELESS, Ltd., RUSSELL, K. A., and MACDONALD, D. A. Dec. 9, 1953 [Dec. 12, 1952; June 3, 1953], Nos. 31599/52 and 15372/53. Class 40 (4). In a wired television broadcasting system the receivers are supplied with video signals, frame deflection signals and a sinusoidal power supply, the last supply forming the sole power supply for the line time-base deflection circuits of the receivers. In the description it is assumed for convenience that the line scanning frequency is 10 kc./sec. First embodiment. The drawing accompanying the Complete Specification shows an arrangement in which the line deflection power is derived from a 5 kc./sec. sinusoidal supply which is locked in phase with television line synchronizing pulses at the central station and applied over leads 50, 51 to step-up auto-transformer 52 tuned to 5 kc./sec. The output is full-wave rectified, the rectifier circuit being completed through a tapped portion of autotransformer 60 tuned to 10 kc./sec., a tapped portion of auto-transformer 61 broadly tuned to 50 kc./sec., and a load resistance 62 which is conveniently constituted by the heater of the cathode-ray tube of the receiver. This circuit is stated to remove about 60 to 70 per cent of the 10 kc./sec. harmonic and about 20 per cent of the 20 kc./sec. harmonic, the remaining harmonic components providing a linear sawtooth wave with a recurrence frequency of 10 kc./sec. Adjustment of condenser 65, resistor 66, and the tapping on transformer 60 provides control of the harmonic components. The unwanted 10 kc./sec. output of transformer 60 may be used to provide E.H.T. Transformer 61 provides the line scan waveform to the deflection plates. Second embodiment. The drawing accompanying second Provisional Specification shows an arrangement in which the sinusoidal supply, which is of the required line scan frequency, e.g. 10 kc./sec., is applied to the primary winding 10 of a transformer having two balanced secondary windings 11, 12 wound in the same sense. The leakance inductance of the secondary windings is tuned to the input frequency by condensers 13, 14, 15, and the outer ends of these windings are connected to ground and one plate of E.H.T. reservoir condenser 16, and to the other plate of condenser 16 and the final anode 17 of the cathode-ray tube, respectively. The windings 11, 12 are tapped at 21, 24, respectively, a first pair of rectifiers 19, 20 being connected between tap 21 and the inner end of winding 12 and a second pair 22, 23 between tap 24 and the inner end of winding 11. A load resistor 25, in series with fixed resistor 26 and adjustably tapped resistor 27, is connected between the junction point of rectifiers 19, 20 and the outer end of winding 12; and a load resistor 28, in series with resistor 29, between the junction point of rectifiers 22, 23 and the outer end of winding 11. The junction points are also connected via D.C. blocking condensers 30, 31, respectively, to condensers 33, 32, the other plates of which are connected to the outer end of winding 11. The condensers 32, 33, in series with 31, 30, form with the load resistors 28, 25 two resistance-capacity time constant circuits and saw-tooth waves in push-pull are developed across condensers 32, 33, and applied to the deflector plates 34, 35. The voltage developed across the reservoir condenser 16 supplies E.H.T. The variable condensers 40, 41 add small portions of the sinusoidal input thereby improving the linearity of the sawtooth output. H.T. voltage for the first anode 42 is obtained at the junction of resistors 25, 26, and the bias voltage for the cathode 43 from the top on resistor 27.