A NEW KEY WEST— HAVANA CARRIER TELEPHONE CABLE 207 



The additional equipment consists chiefly of added receiving 

 ampHfiers and directional filters to care for the greater gain and 

 selectivity needed to operate at the higher attenuation. It includes 

 also equalizers which correct for the varying attenuation of the cable 

 with frequency and a transformer to connect the 600-ohm apparatus 

 to the 130-ohm pair in the underground lead-covered cable. Also, 

 at Key West, a 34-kc. low-pass filter was added to suppress interference 

 from a local radio station having a frequency of about 100 kc. At 

 Havana, a 5-kc. high-pass filter was added to suppress certain relatively 

 low-frequency noises picked up by the circuits in the underground 

 cable. 



ARROWS INDICATE DIRECTION OF TRANSMISSION 

 t HAVANA TO KEY WEST 



12 14 16 18 20 2 2 24 

 FREQUENCY - KILOCYCLES 



26 28 30 32 34 36 38 40 



Fig. 7 — Frequency allocation of communication channels on Key West- 

 Havana cables. 



A photograph of the apparatus installed in the Key West ofifice is 

 shown in Fig. 9. It will be noted that this consists of four "bays" 

 of apparatus, the three nearer of which are practically the same as the 

 carrier equipment ordinarily supplied on long-distance telephone 

 circuits. The fourth bay has the special amplifying and equalizing 

 equipment previously mentioned. A rear view, Fig. 10, shows the 

 interior of one of the special amplifiers, including certain of the special 

 impedance-correcting transformers. Apparatus of a similar nature is 

 installed at Havana. 



Certain Transmission Problems 



Fig. 11 shows the relative energy of the carrier-frequency speech 

 currents as they traverse the circuit from Havana to Key West. In 

 this direction the higher carrier frequencies are employed. Starting 

 from the left of the diagram, the toll switchboard point, which is taken 

 as zero level, the current of a channel sufters a loss of 9 db in a re- 



