ELECT lU C WA\ '!■. - EIL TERS 285 



impedances- at the two mid-points, mid-series and mid-shunt, of the 

 "constant k'' wave-filter of that class. As defined in the first paper 

 referred to, a "constant k'' wave-filter is a reactance network of ladder 

 type, the product of whose series and shunt impedances is k"^ = R^, a 

 constant independent of frequency, where k has the significance of 

 being the impedance of the corresponding uniform line. It is well 

 known that these standard, or "constant k," image impedances vary 

 greatly with frequency over all the transmitting bands and are therefore 

 far from satisfactory as terminal wave-filter impedances. What is 

 needed at a terminal having such an image impedance is a terminal 

 wave-filter transducer of the same class w^hich at one end can be 

 joined without impedance irregularity to the standard termination and 

 which at the other end has a desirable terminal image impedance. 

 Actually, this amounts to terminating a composite wave-filter in a 

 section which has at the final terminals the image impedance desired. 

 We may set up the ideal for this purpose as follows : 



The ideal terminal wave-filter transducer of any class is a dissymmetrical 

 wave-filter network having at one end an image impedance equal at all 

 frequencies to the standard mid-series or mid-shunt image impedance of 

 the ''constant ^" wave-filter and at the other end an image impedance 

 which has approximately the same constant resistance value (k = R) at all 

 frequencies in the transmitting bands. 



^^'hile the principal function of such a transducer is to furnish the 

 desired terminal image impedance, its wave-filter propagation charac- 

 teristics would also be useful. 



The first approximate solution previously obtained was by means of 

 ,l/-type wave-filter terminations;'^ that is, the terminal transducer in 

 this case w^as a single mid-half section of an M-type wave-filter whose 

 parameter m is in the neighborhood of m = .6. Such a section has at 

 one end one of the two standard image impedances referred to above 

 for all frequencies. At the other end its image impedance has the same 

 constant resistance value within about 4 per cent over 86 per cent of 

 every transmitting band and this has proved to be quite satisfactory 

 for many designs. However, later design requirements, such as those 

 for certain low pass and high pass wave-filters in carrier systems, have 

 demanded, principally from an impedance irregularity standpoint, that 

 the resistance terminal characteristic be more nearly constant and 

 extend still farther toward the critical frequencies than is possible with 

 M-type terminations so as to include in this manner a larger part of the 



2 "Transmission Characteristics of Electric Wave-Filters," O. J. Zobel, B. S. T. J., 

 October, 1924. 



^ See page 17 of paper in footnote 1. 



