216 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957 



PULSE ECHO MEASUREMENTS 



Process controls, such as the use of a capacitance monitor and the 

 jointing of the core in manufacturing sequence provided the means for 

 controlling the magnitude of reflections due to impedance mis-matches. 

 However, to insure that the final product met these requirements, 

 measurements of terminal impedance and internal irregularities were 

 made using pulse equipment. 



A block schematic of the circuit of the echo set is shown in Fig. 15. 

 For the submarine cable tests, a 1.5-microsecond raised cosine pulse 



OSCILLOSCOPE 



AND 



AMPLIFIER 



ATTENUATOR 



BALANCING 

 NETWORK 



HYBRID 

 COIL 



-^3C 



PULSE 

 GENERATOR 



REPEATER 



SECTION OF 



CABLE UNDER 



TEST 



Fig. 15 — Simplified block diagram of pulse echo set for measurement of ter- 

 minal impedance and internal impedance irregularities. 



was used, and the impedance of the balancing network was calibrated 

 at 165 kc. The 165-kc impedance of the repeater sections was maintained 

 well within a range of 54.8 =b 1 ohm. The internal irregularities at the 

 point of irregularity were maintained at least 50 db below the magnitude 

 of the measuring pulse. The requirement was 45 db. 



ACKNOWLEDGMENTS 



The authors wish to acknowledge the many contributions made by 

 the members of the staff of the Simplex Wire and Cable Company, 

 Submarine Cables Limited, the British Post Office, and the Bell Labora- 

 tories groups involved during cable design and manufacture. 



REFERENCES 



1. E. T. Mottram, R. J. Halsej', J. W. Emling, and R. G. Griffith, Transatlantic 



Telephone Cable System — Planning and Over-All Performance. See page 7 

 of this issue. 



2. J. J. Gilbert, A Submarine Telephone Cable with Submerged Repeaters, 



B.S.T.J., 30, Jan, 1951. 



3. P. T. Haury and L. M. Ilgenfritz, Air Force Submarine Cable System, Bell 



Lab. Record, Sept., 1956. 



4. H. A. Lewis, R. S. Tucker, G. H. Lovell and J. M. Fraser, System Design for 



the North Atlantic Link. See page 29 of this issue. 



