372 BELL SYSIEM TECHNICAL JOURNAL 



use was made of a rdinluru'd xacuiiiii Uibe aiiiplitier and signal shaping 

 network, the signals being recorded on a string oscillograph. Fig. 6 

 shows part of a test message received over the loaded artificial cable 

 at a speed of 2,240 letters per minute. 



The results of the tests with the artificial loaded cable were en- 

 tirely in agreement with our (■.•ilrnlatinn-; anri showed iliat it was 



Fig. 6 — Test Message. Signals received April 16, 1920, over coil-loaded artificial 

 line equivalent to a 1700 n.m. cable with 30 m.h. n.ni. Speed 2240 letters per minute 



possible to obtain satisfaclor\' signal sliape with a coil-loaded cable 

 having alternating current resistance and distortion factors ap- 

 proximating those of the permalloy-loaded cable. The exact behavior 

 of the proposed cable, including such factors as sea-return resistance 

 and a somewhat \ariable distributed inductance, could not, of course, 

 be duplicated without prohibitive expense. The approximation was 

 considered, howe\er, to be sufficiently good to justif>' proceeding 

 with a loaded cable installation so far as questions of signal shaping 

 were concerned. It is interesting to note that the factor which 

 limited the operating speed of the artificial loaded cable was one 

 which is not present in a continuously loaded cable but which would 

 possiljly be a serious factor in the operation of a coil loaded cable, 

 nameK^he oscillations " resulting from the finite size and separation 

 of the inihu'l.iiu't' units. 



Oi'KR.MioN oi- Loaded Cables 



With the comijlelion of the artificial loaded cable tests there was 

 still one principal question of transmission which had to remain 

 unanswered until a cable had been installed. This was the question 

 of balancing the cable for duplex operation. Ordinary submarine 

 cables are generally operated duplex, the total speed in the two 

 directions being usually from about 1.3 to 2 times the maximum 

 simplex or one-way speed. Except in cases where the external inter- 

 ference is very bad, the limitijig speed of duplex operation is deter- 

 mined by the accuracy with which an artificial line can be made the 

 electrical equivalent of the cable. OrdinariK the aitiliciai line is 



" Carson, Trans. .■X. I. E. E., Vol. iS, p. 345, 1919. 



