Chapter 10 

 SITING 



'"1 GENERAL 



•" ' Introduction 



SITING REFERS to the Selection and utilization of 

 local terrain features which affect propagation 

 and the performance of equipment. From a pre- 

 liminary analysis, the general location, type of 

 equipment, and height may be determined. The 

 specific sites available may, howcA'er, profoundly 

 alter perfomiance in several ways. Careful analysis 

 and tests may then be necessary to determine the 

 best use of the facilities at hand and for an under- 

 standing of the limitations due to the terrain. 



10.1.2 



Siting Requirements 



With communication equipment, the siting prob- 

 lems are principally concerned with visibility and, 

 in wooded areas, absorption by vegetation. When 

 siting direction-finding equipment, it is important 

 to realize that reflections from mountains or other 

 irregularities may cause serious angular errors which 

 should be avoided by proper choice of the location. 

 Both direction-finding and radar eciuipment require 

 orientation. 



Radar siting requirements are rather different and 

 depend on whether ground reflection is of importance 

 or not. The siting of radars operating mainly on 

 the direct ray is relatively easy and is principally 

 concerned with permanent echoes and visibility. 

 The most exacting site requirements are presented 

 by the VHF early warning and height-finding radars, 

 which to a large extent depend on ground reflection 

 for successful operation. The siting problem then 

 requires the consideration of terrain effects such as 

 limited reflection areas, cliff edges, obstacles, etc., 

 which involve diffraction problems of considerable 

 complexity. Recommendations for specific sets are 

 given in instruction manuals furnished with the 

 equipment. 



10 2.1 



TOPOGRAPHY OF SITING 

 Maps 



grid for plotting purposes. The grid location, height, 

 and orientation of each station must be known vcith 

 reasonable accuracy. Topographic maps of a scale 

 of one or two miles to the inch and contour intervals 

 of not more than 100 feet, preferably 20 feet, should 

 be secured. These may be .supplemented by aerial 

 photographs and sur\'eys. 



Radar and direction-finding systems, \\hich may 

 cover a large area and invoh-e many services, use a 



10.2.2 



Profiles 



In a complicated terrain, it is usually necessary to 

 have profiles on several azimuths to determine the 

 effective height above the reflecting surface. The 

 accuracy required decreases with the distance from 

 the transmitter. In most cases sufficient detail is not 

 available on maps, so that a personal inspection of 

 the terrain should be made to become familiar with 

 the nature of the soil and degree of roughness. 

 Special attention should be given to ridges, flat 

 areas, bodies of water, distance to the shore, hills 

 to the rear, obstacles in the operating area and 

 at the boundaries. 



10.2.3 



Orientation 



Where long distances and directive beams are 

 involved, fairly accurate orientation of the order of 

 one-half degree is required. Care must be taken when 

 using compasses because of local attractions or 

 inadequate information on declinations. Observa- 

 tions on Polaris give the greatest precision but this 

 star is not always visible and it is often inconvenient 

 to use a transit at night. Caution must be used in 

 aligning on permanent echoes, as they may be diffi- 

 cult to identify. In general, several methods should 

 be used to obtain independent checks. 



Solar azimuths, correct to the nearest quarter of a 

 degree, may be determined from the date time to the 

 nearest minute, and the latitude and longitude to 

 the nearest degree. Two methods will be given for 

 obtaining the azimuth of the sun: (1) by calculation, 

 (2) from tables. A third method gives true south 

 only. 



187 



