Patent GB-190321088-A (GB)
Title: Improvements in & connected with Telephone Connections on the Party Line System.
Inventor: OPPENHEIMER HERMANN
Filed: 1903-10-01
Granted: 1904-07-14
Abstract: 21,088. Oppenheimer, H., [Akt.-Ges. Mix & Genest]. Oct. 1. Telephone systems; telephone calls.-Relates to party-line telephone systems in which all calls are made through the exchange. In the inactive condition of the partyline a, b, current flows from the battery m at the exchange through the subscribers' stations in series, the circuit being as follows :- Choking coil q', closed-circuit calling drop n, jacks o, p, line a, polarized (alternating current) bell f, " engaged " indicator electromagnet e, hook switch c', line a', &c., the return circuit from the most distant subscriber including a choking coil and line b. -In the case of a call through the exchange, the exchange operator inserts the plug s in the jack p and manipulates the listening and ringing key t so as to put her speaking set z across the cord circuit and connect up with the alternating current selective ringing keys w<1>, w<2>, w<3>. In this position, current from the battery m is still flowing in the line through the choking coil g<3>. If subscriber No. 1 is to be called, the key w<1> is depressed, the continuous current being momentarily interrupted and alternating current from the generator y' sent to line. The bell at station No. 1 alone responds to this current, and in response to the call the subscriber lifts his receiver from the hook. By so doing, he breaks the circuit described above, and de-energizes all the electromagnets e. At the remaining stations, the armatures e<1> fall, and give the "engaged" (arrowshaped) signal, but at the station which receives the call the armature is detained by the contact blocks at the tail end of the hook switch. The microphone circuit k, h, i<1> is thus closed, and the receiver c put to line through the secondary of the induction coil i and the condenser g. The release of the armatures e' at the remaining stations places the condenser g as a shunt to the bell f and electromagnet e, thus removing their inductance from the speaking circuit ; access to the line is at the same time prevented by the removal of the armatures e<1> from within reach of the contact blocks carried by the tail end of the hook switch. The clearing signal, received on the galvanometer u, is given by returning the receiver to the hooks, thus reestablishing the current in the line and energizing the magnets e. Removal of a receiver from the hook gives the call on the annunciator n by breaking the line circuit. When the subscriber to be called is on the same party line, the calling subscriber returns his receiver to the hook after informing the operator at the exchange of the number of the subscriber to be called. That subscriber is then rung up from the exchange, and the removal of his receiver from the hook is notified to the calling subscriber by the appearance of the " engaged" signal. The called subscriber then depresses the key l, temporarily closing the line circuit and causing the " engaged " signal to disappear. The calling subscriber can then remove his receiver from the hook and get access to the line.