206 



BELL SYSTEM TECHNICAL JOURNAL 



^ 35 

 O 



< 15- 



D 



NO REDUCTION 

 SOME REDUCTION 

 LARGE REDUCTION 



i 



^ 



I 



12 3 4 



DEGREE OF SELECTIVE FADING ON HALF-WAVE VERTICAL 



Fig. 12 — Selective fading severity and its reduction at the best positions of the 

 rhombic antenna. Stations GBU and GBW, March and April, 1933. 



Figure 12 is a summary of results of these half-hourly observations 

 made during the working hours of March and April, 1933. Disregard- 

 ing the fact that portions of that figure are shaded, the total lengths 

 of the vertical bars represent percentage of the total number of ob- 

 servations plotted against the degree of the selective type of fading, 

 observed on the comparison antenna, as indicated on the abscissas. 



During each of the above observation intervals, the rhombus was 

 steered over its available range to determine the best position for re- 

 duction in selective fading. Each of the vertical bars in Fig. 12 is sub- 

 divided by shading into the various degrees of fading reduction obtain- 

 able at the best position of the adjustable rhombus. The solid sections 

 represent large selective fading reductions, the cross-hatched sections 

 are fair reductions, while the unshaded portions indicate that the re- 

 ductions were not of appreciable magnitude. 



Analyzing Fig. 12, the results show that 51 per cent of the readings 

 gave no reduction in selective fading; however, for 35 per cent of the 

 readings there was practically no selective fading to be reduced. On 

 the other hand, if one disregards the rather mild and therefore rela- 

 tively harmless fading cases, graded 0, 1, and 2, rhombic fading reduc- 

 tions were possible 89 per cent of the remaining time, so that when 

 selective fading on the comparison antenna was really troublesome, 

 it is important to note that an appreciable rhombic selective fading 

 reduction was nearly always accomplished. By deliberately steering 

 the rhombus to a disadvantageous angle, it was possible four per cent 



