EXPKKIMKVIS IN NORTHWEST 



67 



by very deep lades. This behavior is found in most 

 propagation experiments hut is perhaps rarely as 

 well marked as in this graph. Another feature of 

 interest is the fact that the maximum signal level 

 is fairly close to the free space level. This has been 

 found to hold approximately in a number of other 

 propagation experiments where, in the presence of 

 a duct, the maximum received level seems to occur 

 not far from the theoretical free space signal level. 

 No explanation for this behavior has been given, and 

 it may be purely accidental. 



Figure 1 1 presents, for part of the same period as 



the Canadian Wave Propagation Committee. They 

 were started in the last year of the war and are still 

 under way at the writing of the present report. 

 These tests promise 1 to throw light upon certain 

 aspects of the propagation problem that are difficult 

 to investigate elsewhere. The equipment is located 

 on the prairies of western Canada. The transmission 

 path is over terrain that is as near perfectly level 

 as can be found. The ground is covered with short 

 grass and is without trees or houses. The region forms 

 part of a large flat area in which the atmosphere can 

 be expected to be much more homogeneous than 



-0.1 



k °° 



k AS A FUNCTION OF TIME 

 SEPT I6ANDI8 12 = 00- 18:00 O'CLOCK 





14 



15 16 

 TIME IN HOURS ■ 



Figure 11. Values of A; as a measure of M or N gradient for part of period shown in Figure 10. 



shown in Figure 10, the value of A; as a function of 

 time at a point on the transmission path. Here k 

 is a measure of the slope of the M curve in the lowest 

 strata. Combining equation (17), Chapter 5, and 

 equation (4), Chapter 6, we have l/ka = dM/dh ■ 

 10~ 6 . Thus when k is negative a duct is present. It 

 will be seen that the incidence of negative values of fc 

 correlates well with high signal strength in Figure 10. 



Canadian Experiments 



The Canadian transmission experiments are being 

 undertaken by the Tropospheric Subcommittee of 



in more densely populated regions. Extensive meteoro- 

 logical measurement by means of stationary installa- 

 tions, captive balloons, and airplanes are being 

 carried out simultaneously with the transmission 

 experiments. The path is 27 miles long with receivers 

 mounted on a tower at several altitudes. The trans- 

 mitters operate on the S and X bands and are 

 pulsed. In addition, radar measurements are being 

 undertaken by means of corner reflectors that are 

 spaced at regular intervals along a path 45 miles 

 long. It may be expected that valuable results will 

 soon be received on the completion of these experi- 

 ments. 



