CARRIER TELEGRAPn METHODS 



487 



One-Source Two-Band Method 



This is also a frequency-shift method, and is substantially the same as the 

 two-source method except that a single frequency-modulated oscillator is 

 used at the sending end instead of two oscillators, and thus there is no phase 

 discontinuity in the sent signals. 



^ 35 



O 15 



-300 -250 -200 -150 -100 -50 50 100 150 200 250 300 



FREQUENCY IN CYCLES PER SECOND (FROM MIDBAND) 



Fig. 1 — Loss characteristics of channels tested, including sending and receiving 

 filters and two repeating coils. 



These methods w^ill be more clearly understood from the following descrip- 

 tion of apparatus. 



Apparatus 

 Channel Filter Characteristics 



In Fig. 1, curve A represents the loss vs. frequency characteristic of the 

 majority of channels used in the tests, including both sending and receiving 



