CURRENT coupling circuits are used for the transfer of the carrier energy between the carrier transiitter or receiver and the high-voltage transmission lines. These coupling circuits have taken many forms over the years. Currently, however, there are but two forms: the resonant-tuned circuit and the filter network or broad-band circuit. The increased number of carrier channels which are being installed has increased the attractiveness of broad-band coupling since broad-band coupling has the potentiality of simultaneously coupling many carrier frequencies. It is the purpose of this paper to analyze the performance of broad-band coupling and of resonant-frequency coupling.It is difficult to draw conclusions from the performance characteristics of coupling circuits because these characteristics are, in general, smoothly varying curv es that do not have breakover points.How-ever, this paper wiill reach conclusions which appear to le logical and reasonable. Several of the conclusions make use of characteristics at a line impedance of 200 ohms; however, the line impedances vary over a rather wx ide range and, in so doing, change the perfornance of both broad-band coupling and resonant-tuned coupling. Therefore, an imledance value which seemed reasonable was selected; and, in order that the reader might judge for himself as to the reasonableness of the selection, this paper will discuss this point and others in detail.In addition, there are v ariables which must be defined and accepted in order to accept the final conclusions. However, these variables often are not in themselves provable. For instance, wbhat x-alue of coup)ling loss is accep)table? The only criterion established is that the carrier channel perforni satisfactorily, and this depends not only upon the coupling loss Paper 54-228, recommended by the AIEE Carrier Current Committee and approved by the AIEE
