444 



TABLE 459.— TRANSMISSION FACTORS 163 



Norton calculated from Van der Pol's and Bremmer's theory and checked at broadcast 

 frequencies the following results for vertically polarized ground-wave propagation. In 

 many cases ionospheric waves will be much stronger than is indicated for ground-wave 

 propagation in these tables. Some indication of when ionospheric waves may be expected 

 is given. 



Factor A for transmission over sea water 



6 = 80, O = 5 X mhos/m) 



Freq. 

 Mc 



2 



10 



50 



200 



50 km 



1.0 

 1.0 



.71 



.025 



.00075 



100 km 



.96 



.77 

 .46 

 .0050 



150 km 



.90 

 .72 

 .33 



.0016 



Factor A for transmission over good ground 

 e = 15, a = 10" 2 mhos/m 



Factor A for transmission over poor ground 

 e = 5, o- = 10~ 3 mhos/m 



CRITICAL FREQUENCIES AND MAXIMUM USABLE FREQUENCIES FOR RADIO 

 TRANSMISSION BY REFLECTION FROM THE E AND F 2 LAYERS OF THE 



IONOSPHERE 



Values of ionospheric critical frequencies and virtual reflection heights for all iono- 

 spheric layers (E, E u F 2 , E,) observed at a large number of stations are regularly dis- 

 tributed by the Central Radio Propagation Laboratory of the National Bureau of Stand- 

 ards to laboratories cooperating in ionospheric research. The values presented in Tables 

 458 and 461 are synthesized from the trends of these data. Values are not given here for 

 the Fi and E, layers since their trends are much less accurately established than those of 

 the E and F 2 layers. 



Table 458 presents £-layer maximum usable frequencies for a transmission distance of 

 2,000 km, the maximum practical distance for 1-hop transmission by means of £-layer 

 reflection. 



Table 461 presents F 2 -layer ordinary-wave critical frequencies, and maximum usable 

 frequencies for a transmission distance of 4.000 km, the maximum practical distance for 

 1-hop transmission by means of /Vlayer reflection. 



i53Nr> rtori) K. A The calculation of ground wave field intensity over a finitely conducting spherical 

 earth Proc. Inst. Radio Eng., December 1941; Van der Pol. Bal'th, and Bremmer, H., Philos. Mag., 

 vol. 24, p. 141, 1937; vol. 24, p. 825, supplement, November 1937. 



(continued) 



SMITHSONIAN PHYSICAL TABLES 



