Patent GB-985578-A (GB)
Title: Television standards conversion apparatus
Inventor: BALDWIN JOHN LEWIS EDWIN
IPC: H04N5/91
Filed: 1962-05-08
Abstract: 985,578. Television. RANK-BUSH MURPHY Ltd. May 8, 1962, No. 17640/62. Addition to 898,723. Heading H4F. Apparatus for television standards conversion includes means for recording television signals upon a tape by means of a plurality of recording transducer means arranged to engage the tape in spaced succession during relative movement between the means and tape, together with means for allowing television signals to pass from an input terminal to one or more of the transducer means in a predetermined order, the spacing of the transducer means, their speed of movement relative to the tape and the times at which the signals are applied to each transducer means being such that there is recorded upon the tape a television signal in which the number of lines per frame differs from that in the signal applied to the input terminal. The invention is a modification of that described in Specification 898,723 from which it differs in that the original signal of one standard is actually recorded as a signal of a different standard. The record tape may comprise a magnetic, photographic or electrographic record medium, although only embodiments based on magnetic tape are described. The general principle of the invention is illustrated in Fig. 1 with reference to a tape 1 traversed in the direction 2 past a succession of recording heads 41-45 which are spaced apart the distance occupied by one recorded line and which (for the sole purpose of explaining the principle of the invention) are considered to be stationary. The signal to be recorded is applied from terminal 5 via an amplifier 6. Where the line frequency is to be reduced, certain lines in each frame of the original signal must be elided, for example in reducing from 625 to 405 lines, 220 lines suitably distributed throughout the frame must be elided. This is effected by appropriate closure of switches 71-75 which apply the input signal to the recording heads. For example if recording is to be effected in sequences in each of which two lines are recorded and then the next one omitted, switch 71 alone is closed for two lines and then opened for one. Thereafter switch 72 alone is similarly operated and so on for subsequent switches. Since during the one line intervals in recording the tape advances through the distance between heads, a continuous record appears on the tape. The Specification includes a detailed sequence of switch closures for converting from 625 to 405 lines. Where the line frequency is increased, it is necessary to increase the number of lines recorded. This is effected by closing two switches during certain line intervals so that two recordings are made of one line. For example, if switches 74 and 75 are both closed during one line, a duplicate recording is made. Thereafter switch 74 alone remains closed until a further duplicate recording is required when switch 73 is also closed. Since the arrangement shown in Fig. 1 would require an impracticable large number of heads, the arrangement described in the parent Specification is used based on the use of a small number of heads, e.g. three, carried by a drum which is rotated so as to bring the heads into engagement with the tape in succession. In a modification, Fig. 2, described for reducing from 625 to 405 lines the recording is effected on tracks transverse the tape. Recording of the original signal which is applied at terminal 41, is effected by heads 44A-44D carried by a drum 45. The tape is traversed by capstan 47 and shaped to contact the drum by conventional means. The heads are spaced apart a distance equal to 2À841 recorded lines and each head creates a new track. A degree of overlap between tracks is provided so that the end of one track is duplicated at the commencement of the next Switches 70A-70D are operated in a sequence similar to switches 71-75 in Fig. 1 so as to eliminate 220 lines in each 625. The transverse tracks thus each comprise only two lines except certain tracks which comprise only one. The tape is read by heads 49A-49D on a drum 48 the heads in this case being spaced 1À841 recorded lines apart because one line in each of 2À841 recorded (i.e. 220 in 625) is omitted. Providing the drum speeds are chosen appropriately the recording and reading drums may have different numbers of heads. The signals derived from heads 49A-49D are fed out via slip rings 50 and switch unit 51 to output amplifier 52 and terminal 53. The operation of the switch unit is such that change-over from one head to the next is effected in the first blanking interval after a head encounters its track. The effect of this is that each head always reproduces an integral number of lines, either one or two, with an average of 1À841.