. Elements of radio telephony . enon of fading, which applies alike toradio-telephone and telegraph signals, is not entirely under-stood, but is thought to be due to reflection and refractionphenomena in the upper layers of the atmosphere. Fig. 49shows a transmitting station A and a receiving station Blocated exactly ten wave lengths apart. Part of the signalreceived at B consists of direct radiation parallel to theearths surface and part is reflected downwards by thereflecting medium R after having been originally radiated TRANSMISSION 111 upwards. Radio waves being of exactly the same nature
. Elements of radio telephony . enon of fading, which applies alike toradio-telephone and telegraph signals, is not entirely under-stood, but is thought to be due to reflection and refractionphenomena in the upper layers of the atmosphere. Fig. 49shows a transmitting station A and a receiving station Blocated exactly ten wave lengths apart. Part of the signalreceived at B consists of direct radiation parallel to theearths surface and part is reflected downwards by thereflecting medium R after having been originally radiated TRANSMISSION 111 upwards. Radio waves being of exactly the same nature aslight waves are reflected by conducting layers just as a mir-ror reflects light waves. We do not know what composesthe reflecting layer but believe that it may be composedof dust or moisture-laden particles. If the distance betweenstations is exactly ten wave lengths, when a positive wave isbeing received at B another positive wave will be just leavingA. If the distance happened to be QJ or 10| wave lengths ref/ecfh^ surface. Fig. 49.—Diagram showing how fading phenomena may be producedby reflection from conducting layers above the earth. then a negative wave would have been received at B whilea positive wave was being radiated from A, or vice versa. If the total effective distance measured from A to R andback down to B is an integral niunber of wave lengths apositive wave wiU be received at B when a positive wave isradiated from A, and the waves reaching B over the tworoutes will add together and produce a stronger signal thanthat due to either of the components. The reflecting layeris apparently in constant motion and if moving upwardswill gradually increase the length of the reflected path untilits effective length is increased by a half wave length. Now 112 ELEMENTS OF RADIO TELEPHONY the wave reaching B by the reflected route will phase with respect to the one reaching B by the directroute and the two waves will be of opposite polarity withrespect to
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectradio, bookyear1922
