Patent GB-773204-A (GB)
Title: Colour television recording and reproducing
IPC: H04N5/92
Filed: 1954-06-23
Abstract: 773,204. Colour television. RADIO CORPORATION OF AMERICA. June 23, 1954 [June 29, 1953; July 1, 1953; July 15, 1953; July 30, 1953], No. 18462/54. Class 40 (3). In an arrangement for recording colour television signals for subsequent reproduction utilizing a magnetic tape, the signals are recorded with component signals on a plurality of parallel tracks. Four embodiments are described. In the first (described in detail below), three tracks are employed recording respectively a luminance signal and two colour-difference signals. In the second, Figs. 3 and 4 (not shown), four tracks are employed recording respectively low-frequency red, green and blue signals and a " mixed highs " signal. In the third, Figs. 5 and 6 (not shown), three tracks are employed to record " Y," " I " and " Q " signals in accordance with the American N.T.S.C. standards. Finally, in the fourth, Figs. 7 and 8 (not shown), three tracks are employed to record red, green and blue signals whilst a fourth track is added for synchronizing signals. In each of the four embodiments a further track is added for accompanying sound. Fig. 1 shows the first embodiment in which the luminance signal Ey and red and blue colour difference signals Er-Ey and Eb-Ey are derived from camera 1 through mixer 4 and applied through amplifiers 6-8 to heads 10-12 recording on tape 21 on parallel tracks 23-25. Audio signals from a pick-up unit 2 are recorded on a fourth track 22. The recording heads are also supplied from standard bias arrangements 31a, 31b and are preceded by erase heads 27-30. Pick-up heads 13-16 are provided for audio and video monitors 32 and 33. In order to stabilize the tape speed, synchronizing signals are separated in unit 20 from the output of one of pick-up heads and compared in phase comparitor 17 with the original synchronizing signals from generator 3 to provide a signal for tape motor speed control unit 18. In the reproducing apparatus, Fig. 2, pick-up heads 60-62 derive the component signals from tracks 23-25 and apply them through amplifiers 35-37 to a blanking unit 39 in which all noise, sync. pulses and other signals appearing in the recorded signals during the blanking intervals are cut out and replaced by new blanking and sync. pulses. This operation is effected under the control of a synchronizing generator 44 which is synchronized by a stable local oscillator 45. Oscillator 45 is also connected to a sampler 41 and provides a sub-carrier of, for example, 3.58 Mc/s. upon which the colour-difference component signals are modulated at 90‹ phase points. Synchronizing generator 44 is also arranged to insert in the standard manner short bursts of the oscillator output on the back porch of the blanking pulses. The resultant modulated subcarrier signals are then combined with luminance signal Ey in adder 42 and applied to a utilization circuit 46. Pick-up head 59 engaging the fourth track 22 derives the audio signals through amplifier 34. Speed control of the tape motor is effected in a manner similar to that employed in the recording apparatus by sync. separator 38, phase-comparitor 40 and motor control unit 43. As an alternative to.modulating the colour-difference signals directly on the sub-carrier, a " matrix" stage may be incorporated to first produce " I " and " Q " signals in accordance with the N.T.S.C. standards. Reference is also made to the use of an arrangement to derive the three original primary colour signals. Specification 753,078, [Group XXXV], is referred to.