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BELL SYSTEM TECHNICAL JOURNAL 



One further point is of interest in connection with the subject ot 

 open-wire attenuation. Inductive or conductive coupling between a 

 pair and the other circuits on the line may result in the absorption of 

 energy in these circuits. Fortunately, the losses due to this cause are 

 small on well transposed lines. On inadequately transposed lines, 

 however, this interaction with other circuits, in addition to producing 

 small losses over a wide range of frequencies, may cause incredibly 

 large losses over a narrow band of frequencies, producing what is known 

 as an "absorption peak" in the attenuation curve. This interesting 



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10 15 20 



FREQUENCY-KILOCYCLES 



25 



30 



Fig. 14 — Absorption peaks on an open-wire pair. 



phenomenon is illustrated in the attenuation curves of Fig. 14, which 

 show how two very pronounced absorption peaks on a line about 300 

 miles in length were smoothed out by the application of improved 

 transpositions. The magnitude of one of these absorption peaks will be 

 appreciated when it is realized that the received power at the peak 

 frequency is about one two-hundredth of that at the adjacent frequen- 

 cies. 



