260 BELL SYSTEM TECHNICAL JOURNAL 



second to the highest frequency possible, the attenuation and delay 

 or time-lag of trains of reversals transmitted over the cable. 



Attenuation was measured by transmitting square-topped reversals 

 of constant voltage and frequency and measuring the received current 

 by means of either an amplifier and thermocouple or an amplifier 

 and the string oscillograph, the latter method being preferable at 

 high frequencies where the effect of interference would prohibit 

 accurate measurement by means of the thermocouple. 



The delay for steady alternating currents was measured by trans- 

 mitting short trains of reversals alternately from the two ends of 

 the cable, the transmitted and received trains at each terminal being 

 recorded by means of the string oscillograph on a continuous strip of 

 paper. Thus in a single cycle of operations the record at one terminal 

 would show a transmitted train followed by a received train, while the 

 record at the other terminal would consist of a received train followed 

 by a transmitted train. Since a certain time is required for the 

 establishment of the "steady state" condition at the receiving end, 

 it was found desirable to base the measurement of the time of arrival 

 and departure on a point well along in the train, say at the fifth to 

 tenth cycle. The difference in elapsed time between sending and 

 receiving at the two ends of the cable then gave twice the steady-state 

 delay or "time of propagation" for the particular frequency for which 

 measurements were made. 



Both attenuation and delay were measured for several current 

 values and by extrapolation to zero current the values of these quanti- 

 ties corresponding to a very small current amplitude could be deter- 

 mined. Measurements made on cores in the factory under various 

 conditions of temperature and hydrostatic pressure gave a value of 

 capacity for the cable and from this and the measured delay the 

 inductance could be computed. Knowing the inductance and the 

 capacity, the effective resistance of the cable at various frequencies 

 could be computed from the measured values of attenuation, the value 

 of leakance being estimated from factory measurements. This value 

 of effective resistance should agree with the value obtained by adding 

 together the various known components of resistance. Of the com- 

 ponents of resistance, the copper resistance and the resistance intro- 

 duced by the loading material can be computed from measurements 

 made in the factory. The sea-return resistance can be computed 

 from theoretical formulas and the effect of reflections from irregu- 

 larities along the cable can likewise be estimated. 



For the cables on which such measurements have been made, the 

 values of effective resistance obtained from cable measurements agree 



