490 BELL SYSTEM TECHNICAL JOURNAL 



A discussion is given of some observations of signal fading at 

 various wave-lengths which have been reported by other ob- 

 servers, and which are apparently referable to the same mechanism 

 as is here proposed. 



Introduction 



IN an earlier paper ^ experimental data were presented which indi- 

 cated that the transmission of ultra-short-wave signals was de- 

 pendent upon the state of the atmosphere, in particular upon its water 

 vapor content. The present paper contains the results of a continua- 

 tion of this work where a two-year survey of ultra-short-wave trans- 

 mission over a 70-mile (112.6 km.) ocean path was carried out. Trans- 

 mission was had on 106 days during this period. 



In planning this work, preparation was made for seeking a correla- 

 tion between atmospheric structure and signal intensity; but from the 

 very first transmission fading was found, and this fading was so per- 

 sistent and intense that the work became essentially a fading study. 



In the following paragraphs there are discussed, in the order named, 

 Antennas and Locations; Apparatus and Operation; General Charac- 

 teristics of Fading, with samples of records taken; Polarization Effect 

 on Fading, with sample records; Wave-length Effect on Fading, also 

 with records; Distance and Antenna Height Effects on Fading; 

 Frequency Sweep Patterns of Fading, with sample records; and the 

 logs taken during the flights of the U. S. Weather Bureau airplane for 

 taking free air data. The presentation of experimental data is then 

 interrupted to present a theory which explains several of the experi- 

 mental observations. This is followed by further experimental results 

 and checks, and concluding remarks. 



Antennas and Locations 



Figure 1 shows the layout of the radio circuit. The transmitter 

 was erected at Highlands, New Jersey on the edge of a steep hillside. 

 This edge made an angle of about 45° with the transmitter-receiver 

 direction. Below the edge of the hill lay a strip of land slightly above 

 sea level (seven to eight feet) and beyond was Sandy Hook Bay. 

 The altitude at the antenna foot was 119 feet. The antennas con- 

 sisted of a vertical rhombic terminated in its surge impedance with 

 carbon lamps, a horizontal rhombic with the same termination, an 

 unterminated inverted "Vee" antenna and a half- wave doublet. 

 This doublet was equipped with a flexible transmission line which 

 permitted it to be raised to the top of the antenna supporting mast. 

 These antennas were supported on a central 60-foot (18.3 meter) lattice 

 mast surrounded by four 30-foot (9.15 meter) poles. 



I 



