TOI>0(;KAIMIY OK SITING 



115 



diffraction, for which solutions arc well known or 

 may be readily computed. This subject is unfamiliar 

 to most Service personnel; but a working knowledge 

 of the methods of computation may be obtained by 

 anyone who has the usual engineering education. 

 Since it is not possible to anticipate all problems 

 which may arise in the field, a fairly comprehensive 

 discussion of diffraction has been included in this 

 report so that even in the absence of other references 

 the majority of problems may be treated. 



Other important considerations such as orienta- 

 tion, visibility, permanent echoes, interference, and 

 test methods are discussed. There have been many 

 ingenious developments in these subjects in different 

 theaters, and where available they have been 

 included in this report. Only standard atmosphere 

 propagation has been considered. Those who are 

 interested in nonstandard propagation should refer 

 to the articles on this subject published in this series. 



15.3 

 15.3.1 



TOPOGRAPHY OF SITING 

 Introduction 



The performance of equipment which utilizes radio 

 propagation depends upon the character of the inter- 

 vening land or sea and in particular upon the local 

 terrain at the terminals of the propagation path. 

 Siting refers to the general problem of selecting and 

 utilizing available locations for the best operation 

 of the equipment involved. With some types of 

 equipment the effects of local conditions are minor, 

 and with other types the requirements are most 

 exacting. In many cases practical and tactical con- 

 siderations will compel the use of unfavorable loca- 

 tions. Performance may then be considerably below 

 that obtained in the laboratory or under ideal condi- 

 tions, and familiar characteristics may be drastically 

 modified. 



Field personnel are frequently called upon to 

 predict or explain abnormal operation, to devise 

 methods of improving poor performance, and to 

 make modifications to fit local requirements. This 

 discussion will be limited to general principles, and 

 reference is made to the instructions furnished with 

 the individual equipment for specific details. 



Elements of a communication or radar network 

 should ordinarily be viewed as parts of a system and 

 not as isolated, self-sufficient units. From this point 

 of view a site that gives outstanding results would 

 not be satisfactory if it did not help achieve the 



mission of the system. This interrelation between 

 various parts of a system, which may extend over 

 hundreds of miles, raises numerous problems of 

 orientation, visibility, and coverage. 



1332 Maps and Surveys 



Where available, topographic maps of a scale on 

 1 or 2 miles to the inch and contour intervals of not 

 more than 100 ft, preferably 20 ft, should be secured. 

 Hydrographic charts are valuable in coastal areas. 

 If there are no reliable maps, aerial photographs 

 may be used to a limited extent. 



Due consideration should be given to the suit- 

 ability of the map projection for the purposes for 

 which it is to be used. The grid system used for 

 reporting should be based on the Lambert polyconic 

 projection, and not on the Mercator projection. 

 Otherwise important errors in azimuth may occur. 

 This is especially true at high latitudes. If in coordi- 

 nating with other services, such as the Navy, it is 

 required to use the Mercator projection, the transfer 

 from the Lambert projection may be made with a 

 transparent overlay of one grid system on the other. 



A transit and a stadia rod are most useful for 

 orientation, surveys, profiles, etc. Compasses, clinom- 

 eters, and other surveying instruments should be 

 provided. In the absence of some of this equipment 

 much may be done with improvised devices made 

 with plumb bobs and protractors. Rough surveys 

 may be made with only a sketching board and by 

 pacing off distances. Navigation instruments may be 

 used for approximate determination of position. 

 Engineer and artillery publications describe orien- 

 tation methods in detail. Close attention should be 

 given to the grid system used for reporting nets so 

 that all stations are accurately located. Grid errors 

 may be minimized by making all charts from a 

 master copy. 



1533 Profiles 



The height of the center of the antenna should be 

 determined to within a few per cent. The reference 

 level is the main reflecting surface, which is normally 

 the sea. Heights given on maps should be checked 

 against available bench marks and the terrain. 

 Barometers or airplane altimeters are useful for 

 height determinations, but their readings should be 

 corrected for temperature. 



Where the reflection surface is part or all land, a 



