L 



RADIO PROPAGATION 73 



Appendix III 



In using the equations and curves of this paper to calculate the 

 field, the ground constants appropriate to the location of interest 

 should be employed. The literature on ground constants is already 

 large and is continually increasing. An exhaustive summary of this 

 literature would be out of place here, but as an aid to those who do not 

 have available the ground constants of the locality in which they are 

 interested, the following table is presented. 



The first four sets of values have been widely used. The conduc- 

 tivities of grounds 1 and 5 have been accepted by the Madrid Con- 

 ference as representative of ocean water and average ground. The 

 conductivities of grounds 5 to 8 were obtained from field strength 

 surveys. ^^ The conductivities of water 9 to 11 were obtained from 

 sample measurements by Mr. L. A, Wooten of these laboratories at a 

 temperature of 25° C. Both the conductivity and dielectric constant 

 of water vary appreciably with the temperature, approximately in 

 accordance with the relationships 



(T = ff25°(l + 0.02/), 



€ = 80 - 0.4(/ - 20), 



where / is the temperature in degrees centigrade.* The conductivity 

 also varies from place to place in the ocean due to changes in its com- 

 position. The constants of grounds 12 to 15 were obtained from 

 measurements on samples by Mr. C. B. Feldman of these laboratories. 

 The constants of grounds 16 and 17 are typical of measurements made 

 by Dr. R. L. Smith-Rose on English soil.^^ 



In general, both the conductivity and dielectric constant of the 

 ground vary with temperature, moisture content and frequency as 

 well as location. For a more complete treatment and extensive 

 bibliographies see C. B. Feldman ^^ and R. L. Smith-Rose.^* 



Column 6 of Table IV gives the frequency for which Q = I ior 

 each type of ground. At higher frequencies Q > 1 and the ground 

 tends to resemble a dielectric; at lower frequencies it tends to resemble 

 a conductor. 



Columns 7, 8, 9 and 10 give the values of the parameter x of Fig. 2 

 for a distance of 1 km. and the indicated frequency. For any other 

 distance, x is equal to these values times the distance in kilometers. 

 When Q<^1, .r is proportional to the distance and to the square of 

 the frequency. When the frequency is small compared with that 



* The first equation was obtained from the values given for sodium chloride in the 

 International Critical Tables. The second equation is given in the same source 

 for pure water. 



