192 



BELL SYSTEM TECHNICAL JOURNAL 



curves can be computed by means of the well-known formulas for 

 current and voltage conditions in two coupled circuits. 



Before going into the details of these experiments, it is worth 

 while to consider briefly the general relations in\'olved as indicated 

 by the curves obtained with two coupled circuits, each tuned to 

 52,000 cycles. These curves are shown in Fig. 8. The coils used 



Fig. 8 — Curves Showing the Effect of Cciipling Inductive and Capacitive, on 

 .'\iU[)lification Characteristic of Coupled Tuned Circuits 



had an inductance of 10 millihenries and were tuned by conden.sers. 

 The circuit of the apparatus employed in dlitainini; ilic curNos is 

 given in Fig. 9. 



Curve A gi\'es tin- aniplilicition for induciixt' (■(iu])liii,i; aloiu'. 



Curve B is for capacitive coupling alone. 



Curv-e A-\-B is for both capaciti\'c and inductixe coupiinj; aitling 

 each other, each coupling having the same \alue respecli\el\" as 

 in curves A and B. 



Curve A—B is with the two couplings opposing each other and 



Curve C is the same an A—B but with dilTerent \alue of the inductive 

 coupling. 



The curves have the same shape as the well-known resonance 

 curves for two coupled circuits with the oscillator input in series 

 with the primary circuil, where the peak frequencies are gi\en by the 

 following approximate fnrniiilas: 



Iii(lu(ti\e coupling: /' = 



Jo fit _ Jo 



