RECENT DEVELOPMENTS IN LONG DISTANCE CABLES 489 



above circuits. One way of indicating this is by the repetitions occur- 

 ring per unit time in commercial conversations. Assuming present 

 commercial telephone instruments, typical terminal circuit and room 

 noise conditions, following are some estimates on this basis: 



Repetitions per 

 Circuit 100 Seconds 



Loaded New York-San Francisco circuit 3 



Non-loaded New York-San Francisco circuit 2 



Carrier circuit. New York-San Francisco 1 



H-44 cable circuit. New York-San Francisco 1 



H-245 cable circuit. New York- Washington lyi 



H-174 cable circuit, New York-Washington \% 



B-88 cable circuit, New York- Washington 1 



Short Cable Circuits 



Consideration is now being given to giving up the H- 172-63 two-wire 

 circuits in favor of B-88-50 and H-88-50 two-wire circuits. H-1 72-63 

 four-wire circuits were given up some time ago. With the new two- 

 wire circuits the important line constants and circuit characteristics 

 are given in the following table. 



H-88-50 loading is being considered particularly for those repeater 

 sections less than about 40 miles in length while B-88-50 loading is 

 being considered particularly for repeater sections whose lengths are 

 greater than about 45 miles. For intermediate repeater section lengths 

 the choice of loading will be dictated by various considerations appli- 

 cable to the particular circuit layout involved. 



With either of the above two-wire circuits, the following transmission 

 results are anticipated : 



Circuits for terminal business up to about 250 miles in 

 length to have a working net loss at 1,000 cycles of about 

 9 ± 2 db. The frequency range to extend from about 250 

 cycles to some frequency between 2,750 cycles and 3,000 

 cycles. Crosstalk between circuits to exceed 1,000 units in 

 only about 1 per cent of the combinations. Noise measured 

 at the receiving end of the circuit, including "babble," * less 

 than 200 units. 



Circuits for "via" business to be limited to lengths in the 

 neighborhood of 100 miles so that adding a circuit link of this 

 type to a built-up connection will not, in general, add more 

 than about 2 or 3 db to the overall loss. 



* Babble is the name given to the effect produced by a number of different circuits 

 crosstalking into a particular circuit at a given time and producing an unintelligible 

 murmur. 



