LONG DISTANCE CABLE CIRCUIT 



593 



volume indicator, or about 1 milliwatt of average power, the non- 

 linear distortion became inappreciable. As a matter of fact, occa- 

 sional bursts up to at least db were not badly distorted. It may 

 be observed that the — 5 db volume is about 10 db less than repeaters 



CIRCUIT WITHOUT DELAY EQUALIZERS 

 CIRCUIT WITH DELAY EQUALIZERS 



CURVE 



A 

 B 



DELAY AT 

 1000 CYCLES 



.106 SECONDS 

 .168 SECONDS 



O 



z 

 o 

 o 



UJ 



w 



< 



_l 



UJ 



o 



10 



30 50 100 200 500 1,000 



CYCLES PER SECOND 



2P00 



5,000 8,000 



Fig. 22 — Delay characteristics of 2,200 miles of 16-ga. B-22 cable program 



transmission circuit. 



of the same nominal capacity and loading coils of similar character- 

 istics handle without appreciable distortion under regular message 

 telephone circuit conditions. 



The minimum volume which could be transmitted over the cable 

 circuit, which was set by noise and crosstalk picked up by the program 

 circuit, was found to be about — 50 db at the repeater outputs. This 

 means that the volume range carrying capacity of the circuit was 

 about 45 db, just a little more than the figure 40 db which was pre- 

 viously mentioned as a reasonable standard for present-day conditions 

 of broadcasting. If short bursts of music are allowed to go up to the 

 zero volume at the repeater outputs, the system can evidently handle 

 about 50 db volume range. 



Using special pickup apparatus and loudspeakers capable of handling 

 practically the whole audible frequency range, tests have been made 

 over the 2,200-mile looped-back circuit in which comparison was made 

 of the transmission with and without the cable included. When an 



