. The Bell System technical journal . iscrimination in transmittingantennas as a means of reducing interference between congested com-munication channels. While set noise and static are at times important factors in limitingsuccessful short-wave communication, fading practically always pre-sents varying degrees of annoyance. It is really surprising how muchfading can be tolerated without radically affecting speech intelligibility,but for services such as high-grade program transmission where natur-alness is also important vast improvements are required; consequentlymuch attention has been, and
. The Bell System technical journal . iscrimination in transmittingantennas as a means of reducing interference between congested com-munication channels. While set noise and static are at times important factors in limitingsuccessful short-wave communication, fading practically always pre-sents varying degrees of annoyance. It is really surprising how muchfading can be tolerated without radically affecting speech intelligibility,but for services such as high-grade program transmission where natur-alness is also important vast improvements are required; consequentlymuch attention has been, and is being paid to this phase of the problem. Increasing the Signal Output of Receiving AntennasUnder conditions of optimum output impedances, the magnitude ofsignal developed at the receiving antenna load is simply a function ofthe ratio of the effective induced voltage to the effective antenna re-sistance. The term effective induced voltage is used, as attention mustbe directed toward proper phasing, where the antenna dimensions are. •B Effects of antenna directivity. an appreciable part of a wave-length or more. Usually at shortwaves, the effective resistance is almost entirely the resistance equiva-lent of the reradiation losses. This resistance can be lowered throughdirectivity, a simple example of which can be illustrated with the aidof Fig. 2. If we can conceive of a point source of radiation at A, equipotentialradiation surfaces would be spherical in shape and symmetrically dis-posed around A. The field intensity at point B would be unaffectedif we had some means of avoiding radiation through the unshaded half 660 BELL SYSTEM TECHNICAL JOURNAL of the sphere, with a consequent saving of half of the radiated instead of saving this energy we added it to the shaded side, theenergy available at B would be doubled. This is a simple explanationof the effect of directivity in the transmitting case. The receiving caseis quite similar. If the transmitter is at B, the e
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
