429,095. Exchange systems. SIEMENS & HALSKE AKT.-GES., Siemensstadt, Berlin. Nov. 7, 1933, Nos. 30959, 30960, and 30961. Convention dates, Nov. 8, 1932, Jan. 20, 1933, and Jan. 24, 1933. [Class 40 (iv)] [See also Group XL] In a telephone exchange system having voice-frequency teleprinter facilities, local telegraphic connections are made over telephone lines only, but for long distance telegraphic connections a purely telegraphic channel between the near and distant exchanges is used in order to avoid the uneconomic use of high grade telephone channels for this purpose. The telegraphic channel may be infra - acoustic, carrier current, &c., but as described double current working is used. Repeater circuits are used at the ends of the telegraphic channel to convert the local audio-frequency telegraphic signals into signals of a type suitable for the telegraphic channel, and vice-versa. The telephone exchanges may be manual or automatic. When the distant exchange is automatic, the outgoing repeater also converts dialled impulses, arriving thereat as voice-frequency impulses, into impulses suitable for the telegraphic channel, while the incoming repeater converts these impulses into ordinary impulses for setting selectors, the conversion being subsequently changed to voice-frequency impulses for the telegraphic transmission. Means are also provided to convert the normal telephone tone signals into signals suitable for the telegraphic channel. In one arrangement, Fig. 1, which shows the network at one end of a telegraphic channel FL, a telephone exchange FOV has purely telephonic subscribers F and subscribers having teleprinter facilities such as FT with a common line for telephony and telegraphy, and subscribers FTD with separate lines for these facilities. Telegraph connections between subscribers FT, FTD and similar subscribers on nearby telephone exchanges are set up over the telephone network. A long distance call over FL is set up over a trunk telephone exchange FFV. The call comes in on jack OK and is extended over a normal telephone cord AS to jack FK terminating the line FL, the terminal apparatus including a repeater TU for impulse conversion as above mentioned. The telephonic and telegraphic calls at FFV may be dealt with at the same operators' positions, but the telegraphic duties may be separated and dealt with by a purely telegraphic operator at TFV, selection between the telephone and telegraph operator being made over switch W. TFV may be a telegraphic exchange. The repeater TU may be in the cord circuit in which case separate telegraphic cords must be used. In another arrangement, repeater TU is situated on the line side of jack OK in which case normal telegraphic cords are used and these may also serve for making purely telegraphic connections. In these arrangements, the telegraphic channels may be of different kinds such as infra-acoustic, carrier, &c., and in order to be able to use uniform cords, a further conversion occurs at the outgoing end of the channel. The arrangement described in detail below with reference to Fig. 6, corresponds to Fig. 1 as regards the arrangement of the repeaters, but the operator at TFV transmits impulses to complete the connection automatically at the distant end of the telegraph channel FL which comprises the two one-way lines LI, L2, Fig. 6. Outgoing call. The calling line from TS is extended over one or more group selectors WSI to an idle jack AK lighting lamp AL which the operator answers with plug AS. After ascertaining the calling subscriber's requirements by throwing key ABI and connecting up her set SP, the operator plugs VS into jack VK of the required junction whereupon Y(i) and SV pull up over the sleeve. Y opens the b wire of the circuit for incoming calls (group selector IGW). Engaged junctions may have busy indicators, or busy tone may be applied to them. Relay E energizes and connects operating potentials (battery or rectified A.C.) to the valves of repeater TU so that transmitting relay SR in the output circuit of R2 pulls up and reverses current over line L2, but U, short-circuited by Y, remains inert. Relay TR changes over and connects supervisory tone from TQ which is removed by ER, and the consequent reversal of TR when current over line L2 is reversed at the distant exchange to indicate that the distant repeater is ready to receive. The operator who has thrown MS to connect her set to the outgoing junction, throws AB2 on the cessation of tone and commences dialling, the dialled impulses from ni being repeated by N as A.C. impulses from source TQ. The impulses, after passing filter UF are amplified by R1 and, after rectification at TG, are applied to valve R2 so that SR in the anode circuit responds and repeats the impulses as current reversals over line LI. When the connection has been set up and the switch US at the called station operated manually or by time switch operated by calling current, the operator receives a signal as described later and then recalls the calling party if that party has in the meantime hung up his receiver. Outgoing telegraphic A.C. signals pass from subscriber's apparatus TA over group selector WS1, cord-circuit at TFV to the repeater TU where they are rectified and applied by relay SR in the form of current reversals over line LI. Incoming calls. Current-reversal over line L2 due to the operation of the transmitting relay (SR) when the distant repeater (TU) is seized, reverses the receiving relay ER which operates X to complete the circuit from the repeater TU to the group selector IGW. Line relay A (i) pulls up and holds in series with B(i) which opens the sleeve circuit at jack VK to prevent a call in the opposite direction. Relays E,C and V(iii) pull up and E conditions the repeater TU. Relay ER is already in the working condition owing to the reversal of current at the outgoing end of L2 by the distant relay SR. When anode current flows in the output of R2 both SR and U pull up, and relay TR is operated by current reversals over interrupter UK so that tone periods are connected to jack VK to busy it. SR reverses the current on the line LI to operate the distant relay ER. Selecting (double current) impulses are now received and are repeated by ER to relay I and by I to the line relay A which repeats then to the vertical magnet HM of the group selector in series with V(ii), V(i) being short circuited over rotary off-normal contacts wand the circuit of V(iii) being opened at vertical off normal contacts k. At the end of the train, V falls back and rotary magnet DM by interaction with V (i) hunts the switch to an idle outlet, the short circuit on V(ii) being opened at w. Relay P switches through and the succeeding selectors are set on the wanted line in known manner. When the wanted line is rung and the called party replies, he hears the interrupted tone applied by TR under the control of UK and, realizing that the call is telegraphic, operates switch US to connect up the telegraphic equipment which automatically transmits an AC signal. This signal is long enough to de-energize U as well as SR in the repeater TU, and U remains short-circuited over an off-normal contact k of the group selector. Interrupted tone imposed by TR on the line is cut off, telephonic impulse repeating relay I is disconnected, and telegraphic impulses incoming to ER are repeated to TR which transmits them over the switch train to the called station as audio-frequency impulses from source TQ. Release. The calling party restores switch US and replaces his telephone receiver if he has not already done so. The local switches WS1 are released in known manner so that sleeve relay SA falls back and lights lamp SL to inform the operator who takes down the cord circuit but sleeve relay Y holds over winding (ii) and connects A.C. from source TQ over jack contact kk to the repeater TU. Transmitting relay SR falls back and reverses the current on line LI so that the distant relay ER changes over (to the position shown), X falls back slowly and is followed by A, E and C, Fig. 6 now being considered as the equipment at the distant end. Switching relay P falls back at the group selector IGW and rotary magnet DM drives the switch to 11th contacts where it is released. Relay E has deprived repeater TU of operating potential so that SR drops back and reverses the current over line LI to the calling end at which the receiving relay ER restores and short-circuits X which releases Y and E to restore the calling end to normal. Busy and other supervisory signals. If any of the selectors at the incoming end of the line encounters busy conditions, the usual low tone e.g. from BZ at group selector IGW is connected over 11th step spring w to the line. As this cannot pass back over the telegraphic channel (repeaters TU are tuned to a higher audio-frequency), a common busy signal repeater BE is connected up by finder LS which is started when relay U operates on seizure of the repeater TU. Test relay Q connects up an amplifier-rectifier over filter BF tuned to busy tone and applies operating potentials to the valves thereof. The last valve is normally biassed so that relay BR in the anode circuit is not operated but the grid voltage applied by the rectifier in response to busy tone operates BR which connects relay F to interrupter LU. The transmitting relay SR is therefore intermittently shortcircuited to send back impulses to the calling end, the impulses being any desired distinguishing sequence or combination of long and /or short impulses. At the calling end, the signal is repeated by ER to TR which connects the audio - frequency source TQ to the jack VK. The interrupter LU may be dispensed with when the busy signal at the group selector is an interrupted tone. The equipment BE is released when U falls back on reply of the called party. When other supervisory signals are required separate equipments such as BE are used to rep