Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

ISERVICE RANGE OF FREQUENCY MODULATION 209where W = effective watts radiated = power in antenna times antennapower gain over a one-half wave dipole,a-— receiving antenna height infeet,h = transmitting antenna height in feet,D = distance in miles,D h= distance to the horizon in miles = 1.22 \Hi + 1.22 \Z~a~,/ = frequency in megacycles.In comparing the calculated curves with the experimental data,Beverage states that "scattering and absorption, even in open country,1000kj6005400ZOOSIX1006040-kii',Z 4- 6 3 10 IIVALUE OF EXPONENT V?*Fig. 1—Variation of exponent"n" in propagation formula whentransmission is beyond the horizon.tend to reduce the average intensity to something in the order of thirtyto sixty per cent of the calculated value." In the following derivationsan average experimental factor of forty-five per cent will be included totake into account this absorption and scattering.It will be noted that this formula gives the average field intensityand does not take into account fading. More recent work by MacLeanand Wickizer 4shows the range of fading which may be expected forone set of transmission conditions. Thus, for transmission conditionsreasonably close to the case treated by MacLean and Wickizer, thesignal intensities at the fading minimums may be determined by applyinga correction obtained from Figure 12 of the MacLean andWickizer paper which is reproduced herewith as Figure 2. In thepresent paper, the formulas will be derived for the case of the averagesignal intensity and the fading correction will be applied to the examplesgiven.