Patent GB-1122141-A (GB)
Title: Improvements in or relating to telecommunication systems
Inventor: WILLIAMS HENRY ARTHUR
IPC: H04Q3/42
Filed: 1965-01-16
Abstract: 1,122,141. Voice frequency signalling. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. 14 Jan., 1966 [16 Jan., 1965], No. 2042/65. Headings H4K and H4R. In multifrequency code signalling of digits between registers in the same or different exchanges according to the compelled method, that is a digit is transmitted until acknowledged by a return signal, a forward prefix signal is transmitted before each digit signal and is only replaced by the digit signal when acknowledged by a backward prefix signal. A register A (Figs. 2 and 3) when ready to transmit a digit signal to register B (Figs. 3 and 4) operates relay OST which brings up via contact OST2 two relays SE and SF to transmit two frequencies E and F of the six frequencies A to F as the forward prefix signal. At register B two of the receiving relays RA to RF operate exclusively by filters FA to FF in response to the forward prefix signal and relay FP (register B) operates over a relay chain RA2 to RF2 only if the two frequencies of the forward prefix signal have been received. Contact IST3 in this chain is closed upon seizure of register B. Recognition of the forward prefix signal, signified by relay FP, results in the operation of relays SY and SZ over contact FP5 and the transmission of frequencies S and Y, of the six frequencies S to Z, as the backward prefix signal. Register A receives the backward prefix signal on relays RU to RZ by way of filters FU to FZ; the two responding relays RY and RZ operate relay BP (signifying recognition of the backward prefix signal) over a relay chain RU2 to RZ2 only if the two frequencies of the backward prefix signal are received. As the digit is ready for transmission relay DC has been operated, and therefore contact DC1 is closed and due to the now operated contact BP3 the forward prefix signal from register A is removed by releasing relays SE and SF and replaced by the digit signal as determined by controller DSCE activated over contacts DC1 and BP3. The receipt in register B of the digit signal on two of the receiving relays RA to RZ operates the two corresponding transfer relays TA to TF and if relay DOK operates over a relay contact chain TA2, TB2, TB3, TC2 ... TF2 which checks that only two frequencies have been sent excluding the forward prefix signal frequency combination, the corresponding storage relays DSA to DSF are operated via contacts DOK5 and TA1 and the upper winding of the transfer relays. The selector DD selects a fresh set of storage relays for each new digit, which as they operate to store the digit release the transfer relays via contact DSA1 to DSF1. After the digit has been stored and processed controller ASCF is conditioned to send the acknowledge signal, which is by way of an instruction signal such as send next or previous digit or final digit received. As a result, relay CS is operated and via contactor CS2 releases relays SY, SZ which send the backward prefix signal and activates ASCF to initiate transmission of the instruction signal comprising two of the six frequencies SU to SZ. Register A receives the signal upon receiving relays RU to RZ and transfer relays TU to TZ and relay AOK operates over checking contact chain TU2, TV2, TV3 . . . TZ2 to signify that the signal is two frequencies other than the backward prefix pair. Operation of relay AOK allows the storage of the signals in storage relays ASU to ASZ and via contact AOK3 releases relay BP with the subsequent dropping of the transfer relays TU to TZ. The now open contact BP3 causes the digit signal to be replaced by the forward prefix signal frequencies E and F and the controller DSCE releases relay DC. Depending upon the instruction signal stored in relays ASU to ASZ the controller is reset either to end transmission or to prepare for the next digit. In register B the relay FP operates upon recognizing the forward prefix signal (if further digits are required) to release relay CS thereby replacing the instruction signal with the backward prefix signal enabling the register to receive the next digit. If register B had signalled no more digits earth would have been removed from lead ISTL (placed there upon register seizure) to release relay IST so rendering the forward prefix signal abortive and releasing relay CS as above. Register A acting upon this instruction removes earth from lead OSTL (placed there upon register transmission) which releases relay OST to stop transmission of the backward prefix signal. Register A may be arranged to stop digit transmission after a certain number of digits without any instruction from register B. Separate forward and backward transmission channels may be used thereby removing the necessity for filters FLP2 and FHP2. The prefix recognition relays FP and BP may have additional windings to make them slow to operate and render them further speech immune. Reference has been directed by the Comptroller to Specification 952,711.