. Das Bell System technische Journal . Ces bei Feldstärken, die, obwohl oft zu niedrig, um im Allgemeinen nützlich sein, sind ausreichend, um Störungen in anderen Dienststellen verursachen. Diese Situation wird in Abb. 1. Die obere Kurve zeigt die Therelation zwischen Intensität und Abstand; der untere Teil, die Verflechtung dieser Kurve in Bezug auf Empfangsbereiche. Die Abschwächung, die durch die schwere Linie der Kurve verfolgt wird, ist die der Komponente der Theradiation, die direkt entlang der Erdoberfläche propagiert wird. Es ist diese Strahlung, die normalerweise für eine zuverlässige Broadcast-aufnahme verwendet wird. T
1583 x 1577 px | 26,8 x 26,7 cm | 10,6 x 10,5 inches | 150dpi
Weitere Informationen:
Dieses Bild kann kleinere Mängel aufweisen, da es sich um ein historisches Bild oder ein Reportagebild handel
. The Bell System technical journal . ces at field strengths which, although often too low tobe generally useful, are sufficient to cause interference in other serviceareas. This situation is illustrated in Fig. 1. The upper curve shows therelation between intensity and distance; the lower portion, the inter-pretation of this curve in terms of areas of reception. The attenuationtraced by the heavy line of the curve is that of the component of theradiation which is propagated directly along the earths surface. It isthis radiation which is ordinarily utilized for reliable broadcast recep-tion. The shaded portions near the outer ends of this curve are RADIO BROADCAST COVERAGE OF CITY AREAS 119 intended to indicate the appearance of variations in the signal intensitywhich occur at the greater distances, particularly at night, and whichare known as fading. / c / ^-* / en / c / < . * / t_ / ^ / TS / .5 Variable intensity mmmmm^^ ^ at night. ^^ffilllllillllllllllllllUI Distance / Area oF Fair to Poor Reception.. Fig. 1—The attenuation of broadcast waves in reference to the areas served The evidence of recent researches, particularly those made at shortwave-lengths, indicates that these fading variations are due to radiantenergy which has left the earths surface at the radio transmitter andhas been reflected or refracted back to the earths surface from aconducting stratum in the upper atmosphere. At broadcast fre-quencies the reflected wave component is observed at night but hasnot been noticed during the day. At locations close to the trans-mitting station the effect of the reflected component is negligible ascompared with the strength of the directly transmitted waves. At 120 BELL SYSTEM TECHNICAL JOURNAL increasing distances the directly transmitted waves die away to verylow values and the indirectly transmitted waves begin to show upand appear to become controlling at the longer distances. Thefluctuations themselves appear to be due in part, if not e
