The Use of Coaxial and Balanced Transmission Lines in 



Filters and Wide-Band Transformers for High 



Radio Frequencies 



By W. P. MASON and R. A. SYKES 



At the high radio frequencies, filters and transformers become 

 difficult to construct from conventional electrical coils and con- 

 densers, on account of the small sizes of the elements, the large 

 effects of the interconnecting windings and the low ratios of re- 

 actance to resistance realizable in coils. It is shown in this paper 

 that selective filters and wide-band transformers can be constructed 

 using transmission lines and condensers as elements. The ratio of 

 reactance to resistance in these elements can be made very high; 

 consequently very selective filters and transformers with small losses, 

 can be constructed. The effect of the distributed nature of the ele- 

 ments is taken account of in the design equations and methods are de- 

 scribed for obtaining single-band filters and transformers. Experi- 

 mental measurements of such filters and transformers are shown. 

 The experimental loss curve is shown of a coaxial filter used in the 

 Provincetown-Green Harbor short-wave radio circuit for the pur- 

 pose of connecting a transmitter and receiver to the same antenna. 



I. Introduction 



A T the higher radio frequencies, coil and condenser networks become 

 -*- ^ difficult to construct on account of the small sizes of the elements 

 and the large effects of the interconnecting windings. The Q realizable 

 in high-frequency coils is about the same as can be obtained at the 

 lower frequencies but due to the smaller percentage band widths, it 

 is desirable to obtain a higher Q. There has been a tendency to replace 

 coils by small lengths of transmission lines, and these have been used 

 to some extent as tuned circuits, and as single-frequency trans- 

 formers. ^'^-^ 



It is the purpose of this paper to describe work which has been done 

 in constructing selective filters and wide-band transformers from 

 lengths of transmission lines and condensers. Due to the high ratio 

 of reactance to resistance obtainable in both of these types of elements, 



^ "Transmission Lines for Short-Wave Radio Systems," E. J. Sterba and C. B. 

 Feldman, B. S. T. J., Vol. XI, No. 3, July 1932, page 411. 



^ "Resonant Lines for Radio Circuits," F. E. Terman, Elec. Engg., Vol. 53, pp. 

 1046-1053, July 1934. 



^"A Unicontrol Radio Receiver for Ultra-High Frequencies Using Concentric 

 Lines as Interstage Couplers," F. W. Dunmore, Proc. I. R. E., Vol. 24, No. 6, June 

 1936. 



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