Patent GB-671407-A (GB)
Title: Receiving apparatus for telephone calling impulses
IPC: H04Q1/40
Filed: 1949-06-29
Abstract: 671,407. Automatic exchange systems. WESTERN ELECTRIC CO., Inc. June 29, 1949 [June 29, 1948], No. 17206/49. Class 40 (iv). Impulse receiving equipment is disabled for a predetermined period after reception of an impulse to prevent undesired operation of the equipment by the resulting transients. The invention is applied to a system in which the time interval between a " start " pulse and a " stop " pulse indicates the value of the digit. In the embodiment described the transmitted pulse comprises one cycle of 1000 c.p.s. current and at the receiving end the second half cycle is used for registration purposes. 3¢ milliseconds are allowed for dissipation of the transients, a digit n being represented by an interval 3¢ + ¢n milliseconds between the start and stop pulses. The pulses after passing through a limiter, Fig. 2 (not shown), are applied to valve 310 where the negative half-cycle is inverted and applied to a self-restoring gas valve 311. The flip-flop valve 312 normally has its lefthand side conducting and its right-hand side non-conducting, thereby enabling valve 311 to pass the first pulse which is then applied to the flip-flop circuit which changes over for 3¢ milliseconds during which time it disables the valve 311. Subsequent pulses, provided they do not occur in the disablement period, operate in a similar manner. The pulses from valve 311 are applied to a binary counter valve 313 which on start and stop pulses applies respectively enabling and disabling bias via valve 320 to the 2000 cycle multivibrator 321 which thus produces n+7 pulses between the start and stop pulses. On the occurrence of each start pulse the binary counter 313 applies a negative pulse to valve 412 which repeats it as a positive pulse for setting the counting chain 413 ... 416 which acts as a steering circuit. This chain is provided with a contact 417 for extinguishing all the tubes and a contact 418 which is operated to prime the first valve 413 when the chain is to be used. On the first start pulse the first valve 413 fires, primes the second valve 414 and opens the gate consisting of the left-hand half of valve 421 which thereupon passes pulses from the multivibrator 321 to an A-register 510 consisting of a binary counter capable of counting up to 16 pulses. As it may be necessary for this circuit to register 17 pulses, this number is registered by the setting corresponding to pulse 1 which of course is not associated with any number. The second start pulse fires valve 414 which enables the right-hand half of valve 425 to pass pulses from the multivibrator 321 to the B-register 511. Similarly the third digit is passed to the C-register 512. On receipt of a fourth start pulse valve 416 enables the righthand half of valve 422 to operate relay 423 which restores the registers 510, 511, 512 by opening the H.T. supply to the right-hand sides of the counting valves 513, 514 ... The counter valve 313 is restored to normal prior to use of the circuit by the momentary opening of contact 343. The equipment shown has been constructed for registration of the first three digits only of a subscriber's number, but may be modified to register more or less digits which may be at the beginning or in the middle or at the end of the subscriber's number.