Patent GB-1089555-A (GB)
Abstract: 1,089,555. Multiplex pulse signalling. WESTERN ELECTRIC CO. Inc. Nov. 18, 1964 [Nov. 21, 1963], No. 46907/64. Heading H4L. A transmitter comprises means for generating a coded message wave from which a reserved code signal is excluded, means for detecting a preassigned code signal in the message wave, and means for selectively converting the preassigned code signal into the reserved code signal under the control of supervisory information. In one arrangement using a 5-digit code, Figs. 1A. and 1B, the preassigned code (P) is 01111, which is in the centre of the coding range and therefore occurs frequently, and the reserved code (R) is 11111. The reserved code is never used for the coded message wave, but when 01111 occurs in the coded message wave, it is converted into 11111 if a supervisory signal consisting of "1" is to be sent, or remains as 01111 if the supervisory signal is "0". One or more supervisory signals of this type may be sent to indicate to the receiver the inclusion of an extra pulse to correct the pulse rate at the transmitter, or may be used for pulse group framing. Transmitter.-As shown, a p.c.m. signal from a source 11 is supplied to a plurality of series connected delay stages 1 to 4 each having a delay equal to the time interval between successive digits. The presence of code 01111 causes four 1's to be supplied to the AND gate 13 which is enabled by a signal from a timing source 14. The resulting signal from gate 13 is indicated at monitor 15 and is also supplied to an AND gate 17. If a supervisory " 1 " is to be transmitted a signal from source 16 is supplied via AND gate 17 and OR gate 18 so that the R code 11111 is sent. Receiver.-P.C.M. signals from source 21 are applied to a series of delay stages 1 to 4 similar to those of the transmitter, and to an AND gate 22 controlled by timing signals from a source 23 as before. When a sequence of four 1's appear an output from gate 22 inhibits gate 24 for one digit interval so that if the first of the delay stages contains a " 1 " (i.e. the R code has been received) it is supplied to the message receiver 28 as a "0". A signal from gate 22 is indicated by monitor 25, and is supplied to an AND gate 26 together with the output of delay stage 1 to control a source 27 reconstituting the supervisory signal. Modification.-A nine-digit p.c.m. system in which two speech channels and a television channel are combined in time division multiplex is described. In this arrangement four codes are reserved and four are preassigned for each channel, thus enabling a plurality of supervisory operations to be carried out. Instead of replacing the P codes by R codes the procedure is reversed. At the infrequent intervals when an additional pulse is to be inserted into the pulse train a P code is detected and transmitted without change three times to notify the receiver. Otherwise each P code is transformed into an R code. Since the P codes have been selected from near the centre of the coding range a high incidence of P codes at the receiver will indicate a loss of group framing. An intermediate station is described in which one channel may be dropped and another substituted.