Patent GB-399516-A (GB)
Title: An improved communication system for alternative telephone and telegraph service
IPC: H04M11/06
Filed: 1932-04-06
Abstract: 399,516. Automatic exchange systems. CREED & CO., Ltd., Telegraph House, Croydon.-(Teletype Corporation; 1400, Wrightwood Avenue, Chicago, U.S.A.) April 6, 1932, No. 9888. [Class 40 (iv).] In a system in which some substations have telegraph sets as well as telephone sets, the telegraph set is called by dialling a distinctive number which brings into the connection repeaters for translating the telegraph signals into A.C. form (1100 #) at the originating exchange and for re-translating them into D.C. form at the terminating exchange. In the principal system described, a telephone call is set up by dialling two exchange letters followed by a 4-digit number, while a telegraph call to the same line is distinguished by prifixing the letter T and giving a special value to the hundreds digit. In response to the digit T the first selector steers the connection through a telegraph repeater and line switch to another selector of the same rank, while in response to the special hundreds digit the penultimate selector seizes a connector which includes a telegraph repeater and is available only for telegraph connections. In a modification, the first selector drops back on the digit T, brings into its circuit a telegraph repeater, and then responds to the next digit. In another modification, the same connectors are available for telephone and telegraph calls, but in the case of telegraph calls two extra digits are interpolated before the tens digit which cause the connector to drop back and to bring into its circuit a telegraph repeater. Telegraph calls are distinguished on a called line by reversed battery feed from the connector (enabling provision to be made for preventing a telegraph operator from cutting in on a line engaged in telephony) and by the supply of ringing current of comparatively high frequency (100 #) which does not affect the telephone bell but automatically switches the telegraph equipment across the loop. A telegraph call is automatically answered by a device which telegraphs back the designation of the called set. Exchange metering apparatus individual to a calling line records telephone and telegraph calls separately. Provision is made for testing at either substation whether the telegraph equipment at the distant substation is in working condition. Exchange circuits for telegraphy. The connection, Figs. 3 to 6, includes at the first exchange a line switch 7, selector 8, repeater 14, line switch 15, selector 16 and selector-repeater 12, and at the second exchange, selectors 28, 37 and a telegraph connector 53. The operation of the switches in establishing the connection is ordinary and needs no description. If the wanted line is idle 362 locks up and initiates the supply of 100-cycle ringing current, which automatically brings about the bridging of the substation telegraph apparatus across the loop, whereby 342 is locked up to cut off ring- ing current. The connection now includes repeaters at 14, 12, an incoming bridge 43 at the connector, and a bridge 48 across the called line. Two-way telegraphy can now proceed, breaks in the calling line being translated into A.C. impulses by relay 23 of repeater 14 and re-translated by relay 45 at the connector into short-circuitings of the called line, while breaks in the called line are translated by relay 48 into A.C. impulses which are re-translated by relay 411 at the repeater 14 into short-circuitings of the calling line. The first reverted A.C. signal, which follows automatically on seizure of the called line, energizes relay 435 (bridged across the line at the selectorrepeater 12) to lock up 438, which closes circuits to maintain the continuity of the transmission circuit, which would otherwise be interrupted at each forward signal by the repeater relay 211, which copies the movements of 23. If the wanted line had been busy, relay 338 would have been locked up, putting 48 under control of a cam 410 which transmits the telegraph code for the word BUSY, which is printed at the calling station. Release is effected in ordinary manner when the calling loop is broken. Exchange circuits for telephony. In this case the selector 8 is set to a level giving direct access to a selector-repeater 12, and selector 37 is set to a level giving access to a telephone connector of ordinary type, Fig. 24 (not shown), This supplies 16-cycle ringing current which at the substation rings the telephone bell but does not bring the telegraph apparatus into action. On reply of the called subscriber the connector reverses its incoming current and so energizes an electropolarized relay 223, Fig. 4, which cuts out 435 and energizes 221 to repeat the reversal to the calling line for metering purposes. Modified first selector, Fig. 20, available for either telephone or telegraph connections. This operates in the ordinary way for telephone connections. For a telegraph connection the first digit T raises the switch to its eighth level, and as soon as it enters the bank a circuit is closed over 917 for 945, which releases the switch and locks up 950, so that when the switch has been set again by the next digit the connection includes the telegraph repeater shown at the bottom right-hand corner. Modified connector, Fig. 23, available for either telephone or telegraph connections. This operates in the ordinary way for telephone connections. For a telegraph connection two extra digits 22 are dialled and set the switch to a position in which 541 is energized over 515 to release the switch and to lock up 561, 572. The tens and units digits are then dialled to complete the connection, but 561 brings into play the telegraph ringer 565 or busy transmitter 570 instead of the corresponding telephone devices 599, 600. The calling line is connected by 572 to 595 and the called line to 585, and these relays translate the forward and reverted telegraph signals like 45, 48, Fig. 6. Modified telegraph repeater, Fig. 22. In the system described above, an A.C. telegraph impulse is translated as a short-circuit of the terminal line. By the arrangement shown in Fig. 22 it may be translated as an open-circuit, the relay 1006 closing a holding circuit for 1000 at the same time that it energizes 1004 to open the line. Metering. Successful telephone and telegraph calls are separately recorded by the arrangement' shown in Fig. 18, which is embodied in the line-switch circuit 7, Fig. 3. A magnet 741 and relay 727 are included in one line wire. The reversal of line current when a telephone call is answered energizes 727, which energizes the telephone meter magnet 725, which locks itself to the private wire and shunts 741, 727 out of the line. On a telegraph call 727 is not operated but at every dialled impulse and every reverted telegraph signal 741 steps a wheel 745 which eventually closes a circuit for the telegraph meter magnet 726. It is preferably arranged that the signals sent back by the automatic reply transmitter 88, Fig. 7, are sufficient for this purpose. The wheel 745 is held by a detent 760 until the connection is released. In a modification, Fig. 19 (not shown), the wheel 745 is controlled through a slow-release relay so that each dialled digit advances it by a single step. Substation telegraph equipment, Fig. 7. By throwing a key 75 at the calling station a switch 74 is depressed which starts a motor 94<1>, energizes 91 to lock the key, disconnects the telephone equipment, and connects the line through a dial 82, automatic reply transmitter 88, telegraph transmitter 87, printer 86, and polarized relay 85. If a predetermined time elapses without any signals being transmitted, the key is unlocked at 92, this contact being operated by a traveller which is lowered into engagement with a worm drive by operation of the key 75 and relesaed from the drive at every operation of a key of the transmitter 87. At the called station telegraph ringing current of 100 # over wire 4 energizes 379 (which is effectively shielded from telephone ringing current of 16 # by condenser 378) which energizes 382, 383 to depress the switch 74, and 383 remains energized by the polarized relay 85 which is now in the loop circuit. The device 88, which is friction-driven by the motor 941, is permitted by the armature of 383 to make one revolution, and sends back the designation of the called set which is printed at the calling station. If a telegraph operator attempts to cut in on a line engaged in a telephone connection the switch 74 fails to stay down, the circuit of 91 being open at 94 while the current in the loop is of the wrong direction to energize 85, 383. When the telephone or telegraph set is in use a warning lamp 97 or 95 is lit in the other set. Alternatively the telephone hook-switch and switch 74 may each lock the other. Testing the distant telegraph equipment. To test if the distant printer is in working order, the operator presses key 860 and sends the signals "Shift. M." In the printers at both stations the case-shifting mechanism opens contact 83, while the M printing device momentarily opens 84. At the testing station, contacts 83, 84 are bridged by 860, but at the distant station the loop is momentarily interrupted and this effect is transmitted as a telegraph signal back to the testing station, where it acts as an "unshift" signal. The receiving apparatus is of the kind comprising type bars operated by spring-controlled pull-bars selected by slotted permutation bars, and the arrival of a single break not followed by permutation elements (permutation bars unoperated) allows an unshift pull bar to fall into aligned notches to return the platen. The testing operator, observing his platen shift back, knows that the distant printer is in working order.