514 



BELL SYSTEM TECHNICAL JOURNAL 



junction A and the frequency. One of these is a characteristic of 

 the amplifier, the other of the frequency control unit. It is, of course, 

 apparent that the \-oltage across any junction in a transmission system 

 may be taken as a measure of the rate at which energy crosses this 

 junction. Therefore, points of intersection of these lines satisfy the 

 first condition which was imp<3sed upon the oscillating system in 

 order that it should be in stable equilibrium, namely, that the in- 

 crease of power through one portion should be equal to the decrease 

 in power through the remaining portion. Such points of intersection 

 define values for the amplitude of the voltage at the junction A and 

 of the frequency for which this condition is met. Similar pairs of 

 lines, plotted for other values of the amplitude of the voltage at the 

 junction A, have intersections indicating the corresponding fre- 

 quency for which the energy relations are again satisfied. For each 

 of these points, then, the amplitude of the voltage at A, the fre- 

 quency and the ratio of the amplitude at B to the amplitude at .1 

 have the same \alucs for the amplifier unit that they have for the 

 frequency control unit. In liu- <iir\e .4, of l"ig. (j, the first of these 



FREQUCNCy 

 Fit;. 6 — .Amijliluilc and phase ei|iillil)riiini curves 



variables is |)lolted against the second. The curve, therefore, shows 

 (he magnitude of the voltage delivered by the amplifier unit which, 

 for a given frequency of the wa\e transmitted by the system, jier- 

 mits energy equilibrium to be niainiaiiu-d. 



