Patent GB-843489-A (GB)
Title: Improvements relating to conversion of electrical signals from one duration to another
Inventor: GARGINI ERIC JOHN
IPC: H04N7/01
Filed: 1955-09-29
Abstract: 843,489. Secret transmission. ELECTRIC & MUSICAL INDUSTRIES Ltd. Sept. 27, 1956 [Sept. 29, 1955], No. 27685/55. Class 40 (4). [Also in Group XL (b)] Relates to apparatus for converting a signal train from one duration to another in which the signal train is applied to a first delay line whilst a pulse is applied simultaneously to a second delay line and controls the gating of samples of the train from successive sections of the first line in such manner that, when the samples are assembled in a common output, they occupy a period of greater or less duration than the original signal. In accordance with the invention, the operation is carried out in two stages in tandem employing respectively coarse (long duration) and fine (short duration) sampling. The arrangement reduces the total number of gate stages necessary. Reference is also made to the use of more than two stages in tandem and particularly a binary arrangement which involves the minimum possible number of stages. The invention is described as applied to the conversion of television signals of one line scanning standard to another, although it is stated that it may also be applied to reducing the frequency range of signals (e.g. television signals) to be employed in magnetic recording. The signals are first divided into sections and these stretched in duration and recorded on individual record tracks, corresponding sections of successive sequences being confined to the same track. On reproduction, the signal sections are recompressed and recombined in correct order. Fig. 2 shows the first stage of an apparatus for stretching a 70 microseconds signal, Fig. 6 (a), from a 625 line television signal train into a 100 microseconds signal for a 405 line train. The signal is applied to a first delay line comprising five 6 microseconds sections 6 1 , 6 2  . . . 6 5  separated by gate stages 8 1 , 8 2  . . . 8 5 , and simultaneously initiates the production of a 14 microseconds pulse which travels down a second line 9 1 , 9 2  . . . 9 6 , each section of which introduces a 20 microseconds delay except the first and last which introduce delays of 6 and and 14 microseconds respectively. The gates are normally non-conductive and conduct in response to the arrival of the 14 microseconds pulse at their anodes. The gate outputs are derived from the cathodes which are commoned. In operation, the gates open in turn to pass five successive 14 microseconds samples of the signals, the samples appearing however at 20 microseconds intervals so that the signal in the commoned output appears as shown in Fig. 6 (b). This signal is then applied to a second stage similar to Fig. 2 which functions in effect to stretch each 14 microseconds section into 20 microseconds, so producing a final signal as shown in Fig. 6 (c). In order to do this, the delays of section 6 1 , 6 2  . . . 6 5  and 9 1  in this second stage are made 1 1/5 microseconds, whilst the delays of sections 9 2 , 9 3  . . . 9 5  are made 4 microseconds. The gating pulse has a duration of 2 4/5 microseconds. The final signal consists of 25 samples each of 2 4/5 microseconds duration spaced at 4 microseconds intervals. Fig. 4 shows an arrangement for compressing a television picture line of 200 microseconds duration into one of 100 microseconds duration. The signal is fed simultaneously to delay lines 12 and 13 of 90 and 80 microseconds delay respectively and upon reaching the end of line 13 initiates a 20 microseconds pulse which travels down a 100 microseconds delay line 14 opening gates to sample the signals in lines 12 and 13 from the sections indicated. Samples corresponding to successive 20 microseconds portions of the signal thus appear alternately from lines 12 and 13, but overlapping each other in time by 10 microseconds. The signals then pass to 10 microseconds lines 15 and 17 which operate in conjunction with lines 16 and 18 in a manner similar to lines 12 and 13 with line 14. Sampling pulses of 1 microseconds duration are employed with the gates connected at 1 microsecond intervals along lines 15 and 17. The final signal passing to output 19 consists of 100 one microsecond samples consisting of the first 1 microsecond of successive 2 microseconds portions of the original signal.