A CARRIER TELEPHONE SYSTEM FOR TOLL CABLES 



101 



bay, the carrier supply in a second, the group modulator and demodu- 

 lator in a third, etc. The compactness of the equipment makes it 

 possible to mount the modulators and demodulators for 18 channels 

 on one 11 ft. 6 in. bay 19 inches wide. 



Signaling 



The same type of ringdown signaling equipment is used with the 

 channels of this system as with the voice-frequency toll circuits. A 

 1000-cycle tone, interrupted 20 times per second, is impressed on a 

 channel terminal, modulated, and transmitted over the carrier system 

 in the allotted channel band. At the far end, it is demodulated to 

 operate the receiving end of the standard voice-frequency signaling 

 circuit, or to be transmitted along an extended voice-frequency circuit 

 to its terminal. 



Fig. 18 — Vacuum lube test set. 



Telegraph and Program Applications 



Voice-frequency telegraph can be superimposed on any of the carrier 

 channels as is now done on the three-channel open-wire systems. 

 Equipment is being developed to include a program channel on the 

 cable carrier system. This will be done by devoting to the program 

 circuit the frequency space occupied by two of the 4-kc. speech bands. 



