Patent GB-1193024-A (GB)
Title: Video Recording and Reproducing Apparatus
Inventor: WARREN HENRY RAY
IPC: G11B5/03
Filed: 1968-03-07
Abstract: 1,193,024. Television. RCA CORPORATION. 7 March, 1968 [31 March, 1967], No. 11253/68. Heading H4F. [Also in Division G5] To record first and second time correlated signals, such as the luminance and chrominance or the luminance and audio information in a television signal, in a single track of a magnetic recording tape having a coating of magnetizable material, the information contained in the first signal is translated to a range of frequencies higher than the range of frequencies occupied by the second signal, and the second signal is applied to a first recording head which is isolated from and located in advance of a second recording head to which the translated first signal is applied, both heads being arranged to successively scan the same track of the tape, and the relative frequency and amplitude of the second signal together with the gap length of the first head being such as to cause the second signal to be recorded substantially throughout the thickness of the coating of magnetizable material whereas the translated first signal is recorded only in the surface of the coating of magnetizable material. In a first embodiment, Fig. 1, a pair of recording heads 10 and 12 which may be formed as an integral unit (the heads being magnetically isolated from each other by means of shorted copper turns 26, Figs. 2 and 3, not shown) are located at the end of arm 14 for rotation about spindle 16 so that they helically scan the same track of magnetic tape 18. Head 10 (first head) is positioned to scan the tape prior to head 12 (second head). With switches 28 and 50 in the record (R) positions colour signals 30 and 32, which have frequency or phase modulated 36 and 40 two carrier waves of different frequencies are combined 44, amplified 46, and applied with a bias signal 48 (D.C. or A.C.) to the first transducer head 10. The gap length of head 10, the amplitude of the bias and the amplitude of the colour modulated carrier waves are such that the signals penetrate deep into the magnetizable coating of the tape 18. The luminance signal is coupled through a delay line 52 to a modulator 54 wherein it modulates a third carrier wave of higher frequency than the carrier waves from oscillators 38 and 42. Delay line 52 compensates for the differences in the processing time of the chrominance and luminance portions of the television signal, the same delay line being utilized in the reproducing luminance channel. The luminance modulated carrier wave is amplified 58 and passed via a filter 60 to the second head 12 having a relatively short gap so that it is recorded only in the surface of the coating of magnetizable material and thus erases only a small portion of the colour modulated carrier waves. During playback (switches 28 and 50 in positions P) since the first head 10 has a relatively large gap it only resolves the relatively long wavelengths of the colour modulated carrier waves and thus serves to filter the luminance carrier wave, while the second head 12 which has a relatively small gap resolves the luminance carrier wave. One field is recorded per revolution of the heads and the heads are spaced by an integral number of horizontal line periods (preferably one) of the television signal so that if the lower sidebands of the luminance carrier wave corresponding to the sync. pulse components are resolved by the first head 10 then they occur coincidentally with the resolution by the second head 12 of the luminance carrier wave containing the sync pulse information of another horizontal line. Different transducer heads may be used for play-back and the recording may be longitudinal instead of helical. In a second embodiment Figs. 4 and 5 (not shown), audio information is applied to the first head and luminance information to the second head.