1204 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1956 



4KMC 

 9.4KMC 



Fig. 7 — Height run tower with the three standard horns during preliminary 

 studies of the incident field. 



tower was used for this purpose, and the variation of the incident field 

 with height w^as measured before the antenna was erected. Figs. 7 and 

 8 show a typical set up. Height runs were taken at intervals of 15 feet 

 along a line normal to the direction of transmission in the plane which 

 w^ould eventually contain the antenna aperture. The results of these 

 tests showed that the Murray Hill location was satisfactory for the 4 

 and 9.4 kmc sources, with ground reflections giving rise to ±1 db varia- 

 tions with height. In each case several complete cycles occurred in the 

 60-foot height run so that an average signal level could be established 

 Avith an accuracy of a few tenths of db. 



However, at 460 mc the variation with height was about 5 db, and 

 only a portion of one cycle was available, so that the average signal could 

 not be determined. The solution was to bring the source to a location 

 as close as possible to the effective ground reflecting surface. Such a 

 location was found at the far edge of a large body of water lying in the 

 path, and the source antenna was placed in a mobile truck 10 feet above 

 the water and eight miles away. The resulting variation with height was 

 now only about 1 db. 



In all cases the variation of field at right angles to the direction of 

 transmission w^as found to be no worse than ±1 db; thus it was felt that 

 suitable sources for test at all three frequencies were now ready. 



