TRANSFORMER COUPLING CIRCUITS 621 



kilocycles is only 2500 cycles it is considerably wider at 150 kilocycles 

 as one would expect from the equation showing the relation of band 

 width and capacity. This, however, was not an objectionable feature 

 in the circuit in which the transformer was employed. In order to 

 maintain a constant band width irrespective of its location, the 

 capacity must remain constant and the self impedance of the windings 

 and the coupling coefficients changed or the inductance elements 

 maintained at a constant value and the capacities and coupling 

 coefficients changed. 



IV. Conclusions 



Transformer types of coupling circuits having the inductive and 

 capacitive elements proportioned as explained in this paper are 

 essentially band-pass filters and are therefore particularly adapted to 

 high-frequency amplifiers or circuits where it is necessary to transmit 

 efficiently frequencies within a desired band while strongly attenuating 

 all frequencies outside the band. By proper choice of the transformer 

 constants and the condensers it has been shown that uniformly high 

 voltage amplification was obtained over relatively wide frequency 

 bands. It has also been shown that maximum uniform voltage 

 amplification for a given frequency band was obtained when the 

 output terminals of a transformer coupling circuit were terminated 

 only in a condenser. 



A few applications of transformer coupling circuits have been 

 discussed and the individual characteristic shown. It should be 

 understood, however, that these coupling circuits are not limited to 

 the frequency bands illustrated but may be efficiently used at higher 

 frequencies and over wider transmission bands. 



The author wishes to acknowledge the helpful suggestions of 

 Mr. H. Whittle of the Bell Telephone Laboratories who was associated 

 in the development of transformer coupling circuits for purposes 

 described in this article. 



