Chapter 1 

 TRANSMISSION EXPERIMENTS OVER MASSACHUSETTS BAY 



11 MICROWAVE TRANSMISSION IN 1944 — 

 GENERAL DESCRIPTION' 



THIS PAPER describes the general features of the 

 work on atmospheric refraction undertaken during 

 the summer and fall of 1944 ; other papers by members 

 of this group will describe specific phases. The results 

 described must be considei'ed strictly tentative. They 

 are the outcome of a hasty survey of a large amount 

 of experimental data which ceased to accumulate 

 only a short time before this report was prepared. 

 Consequently, it has not been possible to do more 

 than abstract the most obvious information. 



The principal objectives of the present program 

 were : 



1. To study the modification of continental air by 

 the ocean surface and from this study to improve the 

 technique of forecasting modified index curves at low 

 altitudes over water. The reason for the detailed 

 meteorological study is that when beginning this work 

 we believed that the existing ideas of the physical 

 phenomena involved in producing low-level modifi- 

 cation were not on a sufficiently sound basis to allow 

 a direct analytical approach. 



3. To study experimentally one-way and radar trans- 

 mission through the range of refraction conditions 

 varying from substandard to trapping. Particular em- 

 phasis was to be placed on wavelength dependence, 

 and, when possible, information was to be obtained on 

 vertical coverage patterns under these various refrac- 

 tion conditions. 



Radio Program 



The radio part of the project employed a combina- 

 tion of one-way and radar apparatus operating over 

 Massachusetts Bay. Two paths were chosen for one- 

 way transmission; one was the 23-mile path^ from 

 Deer Island (Boston Harbor) to Eastern Point 

 (Gloucester) and the second a 41-niile path farther 

 from the shore line (Eastern Point, Gloucester, to 

 Eace Point, Cape Cod; see Figure 1). Over the 22- 

 mile path, transipission was on S band, while on the 

 41-mile path one-way transmission was on 117 mc and 



on S, X, and K bands. Radar sets on S and X bauds 

 were placed at tlie transmitter site for the latter path. 

 On the short path the terminals were placed so as 

 to give approximately grazing incidence, but on the 

 long path the terminals were well below the horizon. 



»By D. E Kerr, Radiation Laboratory, MIT. 



10 to 90 40 M eo 



Figure 1. Map of the transmission paths. 



At the transmitting terminal of the one-way circuit 

 were two radar sets on X and S bands; from this 

 location they coidd scan the New England coast line 

 to measure signal strength from fixed targets. 



Note that the short path is close to the coast line, 

 while the longer path is considerably farther away 

 and is so located that approximately westerly winds 

 undergo aj^preciable modification by the time they 

 have reached the transmission path. 



^■^■^ Transmitters 



The transmitter for the short path was located at 

 Deer Island about 180 ft above mean sea level and 



