56 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957 



atlantic repeaters. These capacitors have a storage characteristic which 

 varies with the magnitude of appHed voltage, duration of its appHcation 

 and the temperature. 



Because of this, the usual methods of fault location are expected to 

 give results of doubtful accuracy and so a new approach is being made 

 to the problem. The results of the work to date are beyond the scope 

 of this paper. 



Location of Transmission Faults 



The previous section deals with the situation where the dc power loop 

 has been opened or disturbed. Of equal importance is the location of 

 transmission faults when the power loop is intact. 



For this purpose, use is made of the discrete frequency crystal pro- 

 vided in each repeater.^ This crystal is effectively in parallel with the 

 feedback circuit of the amplifier, and at its resonant frequency the ampli- 

 fier has a noise peak of the order of 25 db, with an effective noise 

 band of about 4 cycles. When one repeater fails, it is possible to recognize 

 the noise peak of each amplifier from the receiving end back to the failed 

 unit. The noise peaks from the faulty unit and all preceding amplifiers 

 will be missing, indicating location of the trouble. Noisy amplifiers can 

 be singled out by an extension of the technique. 



Testing and Maintenance 



Routine testing and maintenance activities at Oban and Clarenville 

 can be divided into four parts: for the carrier terminals, for the station 

 power equipment, for the cable current power units and for the high 

 frequency hne. Usual methods apply and the usual types of existing test 

 equipment were provided with one exception. 



The exception is a newly designed transmission measuring system. 

 The system employs a decade type sending oscillator with continuous 

 tuning over the final 1-kc range. Provision is built-in for precise calibra- 

 tion of output level. The receiving console contains a selective detector 

 functioning as a terminating meter of 75-ohm input impedance, and can 

 measure over the range — 120 to dbm. Coils are supplied to permit 

 measuring over 135-ohm circuits. The detector can be calibrated for 

 direct reading when used as a terminating meter. 



The system covers a frequency range of 10 kc to 1.1 mc. It is useful, 

 therefore, for measuring much of the standard British and U.S. designed 

 carrier terminal equipment as well as for normal line transmission meas- 

 urements over both' the North Atlantic and Cabot Strait (Newfound- 

 land-Nova Scotia) submarine lines. 



