THE RING ARMATURE TELEPHONE RECEIVER 



121 



izing flux of the permanent magnet. Superimposed direct-current character- 

 istics are shown for both the Ul and the HAl receivers in Fig. 9. The verti- 

 cal Une in the plot labeled zero represents the normal operating condition of 

 the receiver with no direct current in the coils. Increasing values of opposing 

 current are plotted to the left and increasing values of aiding current are 

 plotted to the right of this axis. In order that such curves may be compared 

 fairly, they have been plotted on the basis of equal impedances for the two 

 instruments, and each receiver has been referred to an impedance of 100 



76 



74 



72 



Sn_ 70 



hi 

 Q 



o 



? a 



III 



ai Q. 



60 

 0.20 



16 0.12 0.08 0.04 0.04 0.08 0.12 0.16 0.20 0.24 0.28 

 SUPERIMPOSED DIRECT CURRENT IN AMPERES 



Fig 9— Available power response versus superimposed direct current characteristics 

 measured from a source impedance of 128 ohms on a 6 cc. coupler at 1000 cps. Each re- 

 ceiver has been referred to 100 ohms impedance by multiplying its current values by 



/■^lOOO. 



y 100 



ohms. Thus, if both receivers were of 100 ohms impedance at a frequency of 

 1000 cycles per second the curves would be compared directly. If an instru- 

 ment has an impedance differing from 100 ohms, its direct current values 

 along the scale are multiplied by a suitable scale factor as follows: 



1 r ^ . /^lOOO 



Current scale factor = /!/ -^ 



where Ziooo is the magnitude of the receiver impedance at 1000 cycles per 

 second. 



