Patent GB-379754-A (GB)
Title: Improvements in and relating to telegraph systems adapted for conference connections
IPC: H04L12/18
Filed: 1931-06-05
Abstract: 379,754. Telegraph exchange systems. SIEMENS & HALSKE AKT.- GES., Siemensstadt, Berlin. June 5, 1931, No. 16469. Convention date, June 7, 1930. [Class 40 (iii).] In apparatus for effecting conference-circuit connections at a telegraph exchange, means are provided for preventing a sending station from having its own signals repeated back to it. Conference circuit at manual exchange. The in lines from several subscribers terminate in plugs h1 .. h5 while the corresponding out lines terminate in plugs r1 .. r5. When the lines are disconnected, polarized armatures s1 .. s5 are retained in the positions shown by current from battery B1; whereas when plugs h1 .. h5 are inserted, the spacing potential on the lines produces the same effect. When a subscriber T1 is sending, his signals are passed on by relays TE1, S1, and relay-armature s<1>, through coils E1 .. E5 in parallel of sending- on relays. The armatures e2 .. e5 send on the signals through plugs r2 .. r5, and relays similar to TS1, but in order that relay E1 may not respond to signals from subscriber T1, an opposing winding EH1 overpowers the operative winding E1 and so prevents the armature el from responding. Similar coils EH2 .. EH5 are provided for the other subscribers. Resistances are inserted as shown to equalize the impedances facing the relay armatures. Junction-working with conference circuits. Subscribers may be connected to the conference circuit through local exchanges, Fig. 2 (not shown) and may use d.c. or carrier-current channels. Two conference-circuit systems, as shown in Fig. 1, may be connected together, each functioning as one of the other's subscribers, Fig. 3 (not shown). Conference circuit at automatic exchange. Fig. 4 shows a conference group of stations Ta, Tb, Tc .. and also the circuits of a preselector VWa for one station Ta of the conference group. The group may be called by an outside station or by one of its own members through the group line selector LW ; and station Ta may be called independently of the group by an outside station via the selector LWa. Thus the receiving relay ERTa and sending-on relay SRTa of station Ta can be connected to a station external to the group either via the group or line selector LW if Ta is the calling station or via the selector LWa if it is the called station. For conference working it is connected to the other stations Tb, Tc .. of its group via contacts ual, ua2 if it is called or via group or line selector LW if it is calling. When Ta calls, its exchange relay ERTa operates, energizing X and therefore R, which holds on. The stepping magnet D consequently operates the arms of the preselector VWa until a free group or line selector LW is found, whereupon test relay Pa pulls up. Station Ta obtains access, through selector LW, to a sending-on relay SR and to the main winding E and auxiliary winding EH of a receiving relay, these two relays forming part of a conference group Ea, EHa, SRa ; Eb, EHb, SRb ... Relays Ub .. operate in response to potential supplied over the test line c, and their contacts corresponding to ua1, ua2 connect their stations into the conference group ; but relay Ua of the calling station Ta is cut off at pa1 by the test relay Pa, so that station Ta may not be doubly connected to the conference group, a compensating resistance CRa being provided. If station Ta receives a call while connected to the conference group as above, it is marked busy against the new call by its test relay Pa, in the orthodox way. If station Ta has been connected to the conference group via contacts ua1, ua2, in response to a conference call emanating from another station, it is marked busy by contact ua3 which cuts off the test relay Pa. If a conference call is received by a station which is already engaged with a single other station, the call is rendered ineffective by the opening of contacts pa2, pa3. At the end of a conference in which station Ta has been a called station and therefore has been connected through contacts ua1, ua2, the relay SRTa receives a momentary restoring impulse via pa3, ua2, r4, since the relay R is a slow-release relay.