Patent GB-726313-A (GB)
Title: Improvements in or relating to electric circuit arrangements for decoding pulse codemodulation signals
IPC: H03M1/00
Filed: 1953-12-10
Abstract: 726,313. Electric selective signalling. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Dec. 10, 1953 [Dec. 13, 1952], No. 34420/53. Class 40 (1) [Also in Groups XL(b) and XL(c)] Relates to communication systems in which each binary code group of n pulses, representing a given signal or signal amplitude, is selected from a binary pulse sequence such as 00010111, when n = 3, and comprises a decoder for such groups when each is preceded by a distinctive start pulse. At the receiver, the start pulses, the 0-pulses and the 1-pulses are separated and applied respectively to terminals 2, 3, 4 of the decoder. The 0-pulses are applied to 0-relays and the 1-pulses to 1-relays arranged in a closed chain 5 ... 12 in the order of the key sequence 00010111, over leads 20, 21 respectively. Each relay, which in the embodiment described consists of a thermionic valve or the like, responds to produce an output pulse if it receives a code pulse when it has also received a conditioning pulse. The latter is arranged to last only long enough for one response to occur. Just before the first code pulse arrives all the relays receive a conditioning pulse over lead 18, from a generator 19, controlled by the start pulse at terminal 2, so that the four appropriate relays respond to the first 0-pulse or 1-pulse of the group. Delay circuits 5a ... 12a are connected between the relays, and all responding relays send a conditioning pulse through a delay circuit to the next relay enabling it to respond to the next code pulse it receives. The second pulse is thus able to cause two relays to respond, which pass on delayed conditioning pulses to the adjacent following relays. When the third and final code pulse arrives only one relay is in a condition to respond and produce a pulse in its earthed output circuit marked with a X such as 22. This final responding relay'is thus determined by the code group. The connections required for determining the key sequence upon which the code is based may be incorporated in a multiple plug 23 which may be changed to adapt the decoder for other sequences. The output of the decoder may be used to operate electromagnetic relays for separate letter or sign mechanisms of a typewriter, or to produce time or amplitude modulated pulses. In the first example all the pulses of each individual output circuit are fed to an individual gate circuit connected to an electromagnetic relay, the gating circuits being rendered conducting simultaneously, by a pulse derived from the start pulse and occurring when the final decoding relay responds, so that only the appropriate magnet is energized, Fig. 5 (not shown). When amplitude-modulated output pulses are required, all the decoding relays produce output pulses of different amplitude, Fig. 7 (not shown). Time-modulated pulses are produced by connecting the decoding relay outputs to different tappings on a delay line, Fig. 6 (not shown).. Suitable triode and heptode decoding relay circuits and delay networks are described in connection with these last two embodiments.