TELEPHONE EQUIPMENT FOR LONG CABLE CIRCUITS 135 



testing equipment in a large installation. This close association of 

 the composite ringers with the jacks and testing equipment is ex- 

 pected to be of considerable advantage in facilitating the maintenance 

 of the apparatus. 



The need in cable systems of a particularly well-regulated source 

 of 135-cycle signaling current, with sufficient capacity for a large 

 number of lines, has made it desirable to undertake the development 

 of both a special type of interrupter and a motor-generator for this 

 purpose. Close frequency regulation is also very desirable in signaling 

 over cable circuits, in view of the increased sensitivity in receiving 

 which may be obtained by the use of very selective receiving apparatus. 



Fig. 23 shows the circuit arrangement of the interrupter which is 

 expected to be provided for this purpose. This includes a vibrating 



Fig. 23 — 135-Cycle Interrupter Circuit — Simplified Diagram 



reed actuated by an electromagnet when direct current is applied. 

 The contacts on the reed being in series with the battery circuit, 

 intermittent operation is secured in the manner of an ordinary 

 buzzer, the speed of operation for a given applied voltage being de- 



Fig. 24 — Assembly of Vibrator for 135-Cycle Interrupter 



termined by the natural period of the reed. The actuating circuit 

 of the vibrator also includes the primary side of a transformer, the 

 secondary side of which is connected to a filter for suppressing har- 

 monics in the output. The maximum output capacity of the inter- 

 rupter is about three-fourths of a watt. 



