ONE-WAY TRANSMISSION EXPERIMENTS OVER THE SEA 



21 



signal k'\el is liigluT I'oi' :ill riv(j[iit'ueit's wlieii the layer 

 is low and also that the fading range is smaller under 

 these coiiditious. Per a given elevation of the layer the 

 fading range is greater for the higher frequencies. 



Figure 4 shows the character of the signal received 

 on the one-way link when the inversion was low and 

 trapping was definitely indicated by the modified in- 



ing layer al)u\e llie eaj'th. The degree of trapping 

 depends upon the number of modes, or eigenvalues, 

 allowed under the given boundary conditions. 



The San Pedro to San Diego continuous transmis- 

 sion link yields data which can be compared with the 

 simple wave guide theory. The 52-mc data are of par- 

 ticular interest, since for this frequency no meteoro- 



80 MILE LINK SAN PEDRO TO SAN DIEGO 

 TRANSMITTER AND RECEIVER AT 100 FT ALTITUDE 



4000 



j^„....^^g^^||^_,___„.. 



-.^- 



LJiljL*. 



«-- 40 



100 MC ^L 



; 0-; 



IMlfclltLlfell J JtiUiU I 



mi^MC^yCf^fMt^^'nffT^ . 



~1 



S 10 15 20 25 30 



SFPTPU BER OCTOBER 



Figure 3. Maximum signal and fading range related to height of base of temperature inversion. 



dex curve. Figure 5 shows the signals under the con- 

 dition of a high inversion. The time scale is shown 

 along the horizontal at the top of 547-mc tape and at 

 the bottom of the .52-mc record. For the condition of 

 a low layer and strong trapping the level of all the 

 signals is high and the lower frequencies are quite 

 steady. As the elevation of the layer increases the 547- 

 mc signal decreases below detection, the lower fre- 

 quencies become less steady and the maximum level 

 decreases. Figure 5 in contrast with Figure 4 clearly 

 demonstrates this situation. 



Wave Guide Theory 



According to the simple wave guide theory, using 

 the modified index, trapping can occur only when 

 Ail/^0; and then only when the wavelength is suffi- 

 ciently small compared with the height of the reflect- 



logical data have been taken which would indicate any 

 modes allowed. Yet the field strength has varied over 

 a range of some 30 db, the strongest fields occurring 

 at times of high fields on the 547- and 100-mc links. 

 Figure 6 shows the variation of the maximum field 

 strength of the 547- and 100-mc frequencies versus 

 the number of modes allowed as calculated from the 

 meteorological data. There is no apparent correlation 

 at either frequency. 



Eeflection Theory 



It has been shown theoretically^ that reflection from 

 a nonhomogeneous stratum may occur, even when both 

 the index of refraction and its gradient are continu- 

 ous functions through the layer. The controlling fac- 

 tor, for a given incident angle, is the ratio of the 



