Patent GB-496907-A (GB)
Title: Improvements in semi-automatic telephone systems
IPC: H04Q3/00
Filed: 1937-11-23
Abstract: 496,907. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON. Nov. 23, 1937, No. 32219. Convention date, Nov. 23, 1936. [Class 40 (iv)] In a system comprising a local battery satellite exchange controlled from a main exchange, the subscribers' calling circuits at the satellite are connected together in parallel and a call causes the subscriber's line to be disconnected from the calling circuit and connected to a common talking circuit extending over the main exchange line. Connection to the common line is effected bv individual relays which in the case of an incoming call are operated by a marker preferably constructed as described in Specification 459,299. Magneto calling current operates calling relay AR in a loop circuit including rectifiers RA, RB which prevent calling current reaching the lines of other subscribers. Relay AR locks mechanically and disconnects itself from the calling line which it connects to common circuit TS coupled to the junction SL so that calling indicator AK is operated by the calling current. Relay ART pulls up followed in turn by IR, RD and finally RAM, which locks mechanically and releases IR, RD. The operator responds by plugging jack SJ and if the wanted party is a subscriber on the sub-exchange, presses key K and dials the single digit number. The impulses are repeated by IR as 60 volt impulses over relay MRV and a simplex circuit to series relay LHR and marker magnet LV at the subexchange. MRU remains inert. On receipt of the first impulse, the marker operates relay UMR which locks mechanically, busies the common circuit to other calling parties by shunting their relays AR over rectifiers RC and short-circuits a condenser C used for improving the transmission of magneto current. The selected line relay AR operates in parallel with the marker magnet and the operator rings over the junction preferably after asking the calling party to replace his receiver. Release. The subscriber's ring-off signal operates an indicator in the cord-circuit, and when the cord is taken down, IR operates over a jack spring and interacts with RD to send further impulses over the junction. When the marker reaches its penultimate contact, UR is operated to release the mechanical locks on relays AR and UMR, and then direct ground on the last contact of the marker operates MRU at the main exchange over the simplex circuit. MRU releases the mechanical lock on relay RAM which stops the impulsing. During release impulsing, RH connects a resistance in parallel with impulse relay IR to control the impulse speed. Busy signal ; attracting operator's attention. When a subscriber calls during a busy condition of the sub-exchange circuits (UMR operated) SR (lower) is operated by rectified calling current and releases a vibrating armature controlling its upper winding to give a busy signal. If the subscriber desires to intimate to the operator that termination of an existing conversation is desired, he sends a long ringing signal in response to which SR connects ground over its lower winding to a simplex circuit in which RG pulls up followed by RF and a relay RI which vibrates an armature to operate the indicator AK. Conference facilities. The operator may by dialling successively say digits 5 and 2 connect subscribers 5 and 7 to the common circuit and in this way two or more subscribers may be connected to a calling party.