Chapter 5 

 TRANSMISSION EXPERIMENTS IN ENGLAND 



SI BRITISH TRANSMISSION 



EXPERIMENTS* 



^■^•} Introduction 



THH BROAD OBJECT of the studies carried out in 

 Great Britain during tlie past few years lias been 

 to establish the characteristic facts of the propagation 

 of centimeter waves (more recently of meter waves 

 also) and especially to determine the relationship be- 

 tween radio performance and meteorological condi- 

 tions in the lower atmosphere, with forecasting as the 

 ultimate aim. 



Although propagation of 10-cni waves to distances 

 much beyond the optical range had been observed 

 under favorable conditions nearly a decade earlier, 

 it was the striking increases in range of decimeter 

 and centimeter wave coastal radars in southern Eng- 

 land, observed in the summers of 1940 and 1941 re- 

 spectively, which led to a concentrated attack on the 

 long-range aspects of the problem. About the same 

 time a need arose for more accurate knowledge of both 

 the short-range "interference" field and the long- 

 range "diffraction" field for certain communication 

 projects, and the radio equipment developed to meet 

 this need formed a nucleus round which the later and 

 more ambitious experiments grew. 



The various experimental and theoretical aspects 

 of this work were reviewed in some detail at the meet- 

 ing of the Ultra Short Wave Propagation Panel under 

 whose auspices the ^\'ork is being done, in London 

 on October 6, 1944; these reviews have been circulated 

 as listed in references 1 throiigh 15. 



Continuous observations have been carried out over 

 a range of optical and nonoptical paths across the Irish 

 Sea on S and X bands and over a single 38-mile land 

 path on S band. These are discussed below. In addi- 

 tion to this work several investigations of more specific 

 propagation problems have been carried out during 

 the summer of 1944. 



1. Measurements on two wavelengths in S band, 

 over a 70-mile sea path between a site in South Wales 

 and the summit of Snowdon (3,500 ft). This optical 

 path was studied to obtain data on the probability 



"By E. C. S. Megaw, Ultra Short Wave Panel, Ministr3' of 

 Supply, England. 



of missing aircraft on S-band radars under conditions 

 favorable to trapping at low levels over sea. 



3. Measurements on a wavelength of about 3l^ m 

 over a 90-mile sea path, with heights such that the 

 path length was about twice optical range, to provide 

 quantitative data on the importance of refraction in 

 this waveband. 



3. Eadar measurements from Llandudno, North 

 Wales, with the Isle of Man and the Irish Coast as 

 the main targets, on S, X, and K bands. The object 

 was to obtain practical data on the relative perform- 

 ance of K band under a variety of meteorological 

 conditions which were studied simultaneously with 

 the radar observations by ship, balloon, and aircraft 

 measurements. Some further reference to the results 

 of (1) and (3) apjjears below; an interim report on 

 (3) has been circulated." 



^•^■^ Irish Sea Measurements 



The first j)lant for simultaneous measurements 

 within and much beyond the optical range on wave- 

 lengths of about 9, 6, and 3 cm, using heights of 

 about 100 and 500 ft each site, was made in the 

 latter part of 1941. 



The work was planned on an inter-service basis, 

 with equipment provided by Admiralty (developed 

 under Admiralty contract by General Electric Com- 

 pany Eesearch Laboratories from that used in the 

 early communication studies mentioned above) and 

 stations jjrovided and operated by Signals Eesearch 

 and Development Establishment, Ministry of Supply. 

 Arrangements were made for analysis of the data by 

 the National Physical Laboratory, which has also 

 more recently undertaken the development of moni- 

 toring equipment. The collaboration of the Meteoro- 

 logical Office was received at an early date, but it 

 was only when the study of the subject had made 

 further progress that the need for detailed low-level 

 meteorological measurements was realized ; these have 

 been undertaken by the Naval Meteorological Service, 

 soundings being made in ships and by means of ship- 

 borne balloons. Additional arrangements have recent- 

 ly been made with the Meteorological Office for regu- 

 lar aircraft soundings over the path. 



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