RADIO PROPAGATION FUNDAMENTALS 



Gil 



cycles appear to be feasible with the antennas that are needed to pro- 

 vide adeciuate signal-to-noise margins. Successful tests of television and 

 of multichannel telephone transmission have been reported on a 188- 

 mile path at 0,000 mc.'' 



The effects of fast fading can be reduced substantially by the use of 

 either frequency or space diversity. The freciuency or space separation 

 reciuired for diversity varies with time and with the degree of correlation 

 that can be tolerated. A horizontal (or vertical) separation of about 100 

 wavelengths is ordinarily adequate for space diversity on 100- to 200- 

 mile paths. The corresponding figure for the required frequency separa- 

 tion for adequate diversity seems likely to be more than 20 mc. 



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DECIBELS RELATIVE TO MONTHLY MEDIAN VALUE 



40 



Fig. 10 — Typical fading characteristics at points far beyond tlie horizon. 



