ULTRA-SHORT WAVE PROPAGATION 127 



explained quantitatively in this way. Reflection, diffraction and 

 refraction all play their parts. 



On the experimental side, the longer distance ultra-short wave 

 transmission studies described in the literature have been made almost 

 exclusively with apparatus capable of making only qualitative measure- 

 ments. In spite of this handicap, many valuable observations have 

 been made.^ The outstanding result of these has been the demonstra- 

 tion of the advantages of an "optical" path, or rather, one in which a 

 straight line between the transmitting and receiving antennas is 

 unbroken by the intervening terrain. In many cases, however, this 

 advantage has been greatly over-emphasized. 



As a basis for studying the relative importance of the various 

 mechanisms that have been suggested, quantitative measurement 

 must replace qualitative observation. Part I of this paper presents 

 some of the results of an experimental study of the propagation of 

 ultra-short waves, made with the objective of obtaining quantitative 

 data of sufficient accuracy to serve as a basis for theoretical work. 

 Part II discusses the theory of ultra-short wave transmission and 

 analyzes some of the experimental results from that point of view. 



Part I — Experiment 



Equipment and Procedure 



A considerable portion of the transmitting in connection with this 

 survey was done with a 1000-watt transmitter located at Deal, N. J. 

 In this transmitter the last stage employed four 1000-watt radiation- 

 cooled tubes as an oscillator at 69 mc. The frequency was controlled 

 by a 3833-kc. crystal oscillator acting through a chain of amplifiers 

 and harmonic generators. A simple vertical half-wave antenna was 

 used for most of the tests. It was located about 60 meters above 

 ground and was driven through a long two-wire transmission line. 

 The stability of this transmitter was a definite advantage and facili- 

 tated the taking of reliable data. Another transmitter of slightly 

 higher power was employed for the lower frequency tests from Deal. 

 Similar antennas were used. 



For most of the over-water tests use was made of a mobile trans- 

 mitter of some 100 watts output, while for some of the very short 

 distance work, a simple portable oscillator using receiving tubes was 

 employed. The radiator, a simple vertical antenna, was located on a 

 wooden tripod on a bluff at Cliffwood Beach, N. J. This bluff over- 



' On account of the extensiveness of these qualitative studies, no attempt is 

 made to give a complete bibliography. A few articles giving results of especial 

 interest in connection with the present paper are cited in the text. 



\ 



