148 



BELL SYSTEM TECHNICAL JOURNAL 



I/) 



2 700 



I 



° 600 



z 



lij 500 

 O 



j< 400 



u 



<300 



a 



a. 200 



UJ 100 



i7)-IOO 



cc 



100 



500 1000 



5000 10,000 



50,000 100,000 



500,000 



FREQUENCY IN CYCLES PER SECOND 



Fig. 11 — Impedance-frequency characteristic of a transformer designed to operate 

 between 600-ohm terminations and to transmit high frequencies in addition to audio 

 frequencies. 



80 

 70 

 60 



50 

 40 

 30 



10 50 100 500 1000 



FREQUENCY IN KILOCYCLES PER SECOND 



5000 



Fii 



J. 12 — Impedance-frequency characteristic of a transformer designed to operate 

 between resistance terminations of 70 ohms and 144 ohms. 



may be provided in many ways in the input transformer, which con- 

 sideration allows much wider latitude in the design than in the ordinary 

 transformer; there the major part of the dissipation for low trans- 

 mission loss necessarily must occur in the load. A typical impedance 

 characteristic of such an input transformer is shown in Fig. 13. 



Testing Precautions 



As a necessary concomitant to improvements in transformers, more 

 precise testing circuits have been developed for accurately determining 

 transformer performance. In estimating the performance of the trans- 

 former from its characteristic, care must be taken to make sure that 

 the service conditions were reproduced carefully in the measuring 

 circuit. In particular, certain precautions must be observed in the 



