The Design of Radio-Frequency Choke Coils

The selection of a choke coil without regard for overtones is likely to permit kinks in the curve of apparent capacitance. These kinks represent overtones, at whose frequencies the choke coil has maximum values of excess shunt conductance, and therefore is unsuited for connection across a sharply selective tuned circuit. These overtones occur near even multiples of the fundamental frequency, in the absence of an iron core. Choke coils of two equal or unequal sections are proposed, and rules are given for proportioning the dimensions to suppress the first and second overtones. Examples are described, in which the remaining effect of the third overtone is small and that of higher overtones is negligible. Iron cores for choke coils have some advantages, in reducing the excess conductance, as indicated by the performance of an example described.