Patent GB-719104-A (GB)
Title: Improvements in and relating to signal transmission apparatus
IPC: H04N11/12
Filed: 1952-03-14
Abstract: 719,104. Television. PHILCO CORPORATION. March 14, 1952 [March 16, 1951], No. 6698/52. Class 40 (3). [Also in Group XL(c)] In a dot-sequential colour-television system the "sampling" of the component colour signals is effected by at least two sampling devices operating in phase quadrature or in phase opposition. Fig. I shows the arrangement empoyed m a two-colour system the two component colour signals being supplied via terminals 20, 22, to valves 10 and 12 respectively which are "opened" for brief intervals by the 0 degrees and 90 degrees phases of a switching wave from a source 16. The signal in the anode circuit of each valve (which have a common anode load impedance 14) comprises pulses 24 and 26 respectively each of amplitude determined by the amplitude of the respective colour-component signal of the sampling instant and each series of pulses is effectively converted into corresponding sine waves (shown at 30 and 32 respectively) by the action of a filter 28 which produces a single resultant sinc wave having an amplitude and phase proportional to that of the (effective) sine waves 30 and 32. The output of filter 28 is then transmitted in any suitable manner and at a receiving position a similar wave is derived, e.g. at the output of unit 40, which is converted into signal wave corresponding to the component signals supplied to terminals 20 and 22. This is effected by supplying the output of 40 to a pair of sampling valves 42, 44 (complementary to valves 10 and 12) operating in phase quadrature under the control of an oscillator 54 of similar frequency to oscillator 16 and then supplying the resulting pulse outputs developed across resistors 46, 48 respectively (similar to the pulse trains 24, 26 respectively) to L.P. filters 56, 58 which produce integration thereof to reproduce the original component signals supplied to terminals 20 and 22, respectively. When the passband of filter 28 and the frequency of oscillator 16 are such that one side-band of the output wave is partially (or wholly) suppressed cross-talk between the two signals may be minimized by limiting the band width of one of the input signals by means of L.P.F. 36 and employing a similar filter 58 at the receiver. In a second embodiment (Fig. 2) allowing the transmission of three component signals two of the signals are supplied via terminals 110, 112 to sampling valves 100, 102 operating respectively at the 0 degrees and 180 degrees phases of oscillator 126 to produce, after transmission through L.P.F. 109, an effective wave 129 and the third signal is supplied, via terminal 114, to a sampling valve 104, operating at the 90 degrees phase of oscillator 126 and, after phase rehearsal in 116, to a further sampling valve 106 operating at 270 degrees relative to produce (after transmission through L.P.F. 109) an effective wave signal as shown at 131. These waves (129 and 131) which are effectively combined by the action of filter 109 are then transmitted in any suitable manner and at a receiver a complementary sampling system comprising valves 142, 144, 146 and 148 controlled by appropriate phases of oscillator 174 (of similar frequency to oscillator 126) recovers the original signals in a similar manner to the arrangement of Fig. 1. In a third embodiment also allowing the transmission of three component signals (Fig. 3) the first signal (supplied to terminal 214) is sampled in valves 200 and 202 at the 0 degrees and 180 degrees phases of oscillator 224 to produce (after transmission through L.P.F. 211) the effective wave 248 and the other two signals (supplied to terminals 216 and 218 respectively) are sampled by supplying each with opposite phases to pairs of valves 204, 206 and 208, 210 gated respectively by the 0 degrees, 180 degrees and 90 degrees, 270 degrees phases of oscillator 224 to produce (after transmission through L.P.F. 211) the effective waves 250 and 252 respectively. A composite wave representing the sum of the waves 248, 250 and 252 (produced by the action of filter 211) is then transmitted and at the receiver a complementary sampling system employing the valves 260, 262, 264, 266, 268, 270 gated by appropriate phases of an oscillator 258 (of similar frequence to oscillator 224) recovers the signal information.