DIRECTIVITY STEERING FOR FADING REDUCTION 199 



A primary essential in this scheme is that no minor ears of the direc- 

 tive diagram be of appreciable size. 



Using this scheme, it is not necessary to discriminate completely 

 against the adjacent waves for practical benefit. A discrimination of 

 ten decibels between two adjacent waves of equal amplitude will 

 make improbable a fade deeper than 5.7 decibels from their sum. 

 Fading of this depth would be relatively unimportant for ordinary 

 speech transmission. 



An edge wave may at times be much smaller in amplitude than the 

 adjacent waves. The scheme under discussion may be usefully opera- 

 tive even in this situation since the very smallness of the edge wave 

 means that it cannot be seriously harmful. When signals are weak, 

 the edge of the directive diagram should be advanced until a large am- 

 plitude wave is encountered. Some fading of small depth would 

 then exist. 



It was stated above that the antenna system used should have no 

 minor ears of appreciable size. At the same time, the edge position of 

 the major loop must be continuously adjustable. A simple method of 

 meeting these requirements is that of mechanically moving the ele- 

 ments of a "long-wire" antenna in space so as to alter the manner of its 

 exposure to the space waves. 



Figure 3 is a rectangular plot of the incident plane directive diagram 

 of a large horizontal rhombic antenna when used for GBW on 20.78 

 meters. The essential antenna dimensions are indicated on that 

 figure as well as the equation for the directive diagram. 



Each bracketed quantity in the directive equation of Fig. 3 is 

 separately plotted on that figure together with the final resulting 

 product. Factor 3, known as the "phasing " factor, exerts the greatest 

 influence on the shape of the major lobe. This factor contains only 

 the variables of length 1 and the angle 0, defined as half of the side 

 interior angle. The length cannot be made easily variable but the 

 angle </> can be readily adjusted. When an adjustment in is available 

 for this antenna. Fig. 4 gives the directions of the major lobe maxima, 

 and the first nulls, above the horizontal for a series of wave-lengths. It 

 is evident that a useful degree of steering is provided without limiting 

 the desirable variable wave-length features of the antenna. In all 

 cases, the minor ears remain small. 



In Fig. 5 is shown a. remote controlled power-winch system for 

 altering the interior angles. This experimental system in slightly modi- 

 fied form was in operation at Holmdel, New Jersey, for some time, 

 without any antenna breakages. This was primarily possible because 

 the angles of flexing were very small and copper-clad steel wire was 



