CARRlER-CURRliNT COMMUNICATION 651 



The general appearance of the carrier s\steni may be seen from 

 Figs. 11 and 12 which show the equipment at San Pedro and Avalon 

 respectively. Fig. 13 is an interior view of the San Pedro cable hut 

 showing the cable terminals, together with the insulating transformers, 

 telegraph composite sets, and basis networks. Referring to the cen- 

 tral office equipment, the first bay contains the equipment for two 

 complete channels. At the top are the terminal strips for making all 

 connections with the equipment below. On the next two small panels 

 are mounted the hybrid coils and the other miscellaneous apparatus 

 associated with the voice-frequency ends of the two channels. Below 

 these are the modulator and demodulator band filters which are 

 covered with dust proof cases. Next comes the modulator and de- 

 modulator panels for one channel. Below the two jack strips is 

 mounted similar equipment for a second channel but arranged in 

 reverse order. In the upper half of the second bay is located a small 

 panel mounting the carrier hybrid coil and associated equipment. 

 Below this appear the transmitting and receiving amplifiers. The 

 lower half of the bay is similar to the lower half of the first one. In 

 the third bay is mounted all the battery supply and testing apparatus. 

 The first two units contain the battery retard coils. Below these are 

 the alarm relays and auxiliary resistances. Next come the meters 

 for measuring the tube currents and voltages, and below these are 

 the thermocouples and artificial lines for making high frequency 

 measurements. Below the jack strip are the keys for opening and 

 closing the individual filament circuits used for measuring the plate 

 and filament currents. Alarm lamps are also associated with each 

 of the filament circuits. The fourth bay is similar to the second 

 except that the upper half is vacant. As may be seen from the photo- 

 graphs, the amplifiers appear on the second bay at San Pedro and 

 on the fourth at Avalon. The fifth bay is an exact duplicate of the 



first. 



The new system has now been in successful operation for the past 

 five months. In the light of its performance thus far, we feel assured, 

 that when more circuits are required a second system of six channels 

 can be added to the second cable, thus providing a total of fourteen 

 telephones and two telegraph circuits over the two single-conductor 

 cables. Such a circuit group, we believe, will meet the traffic re- 

 quirements for quite a number of years. 



