64 



TRANSMISSION EXPERIMENTS 



20 



40 



t- 

 < 



5 

 2 s 60 



"^ UJ 



m 



80 



110 



100 80 60 40 



DB BELOW 1 WATT 

 S BAND 



20 



Figure 5. Correlation between S- and X-band signal 

 strengths, Massachusetts Bay. 



40 



60 



om 



_i 



80 



100 



120 



100 80 60 40 



DB BELOW 1WATT 

 HIGH RECEIVER 



20 



Figure 6. Correlation between signal strengths at high 

 and low receivers, Massachusetts Bay. 



:100 



5 

 o 



to 120 



140 



80 60 40 



DB BELOW 1 WATT 



S BAND 



20 



Figure 7. Correlation between 117-mc and S-band sig- 

 nal strengths, Massachusetts Bay. 



the S-band and 117-mc signal levels, as Figure 7 

 indicates. 



It is hardly necessary to state that the high signal 

 levels occur when the meteorological measurements 

 show the presence of a duct and the substandard 

 signals occur when the M curve is of the substandard 

 type. It will not be possible, in this summary report, 

 to enter into the detailed relationship between signal 

 strength and M distribution. In a general way the 

 experimental results confirm the electromagnetic 

 theory in so far as it has been worked out at present. 



Another aspect of the short wave transmission 

 that has been studied in these experiments is the 

 relationship between radio and radar transmission. 

 Since radar involves two-way transmission, its path 

 factor, as defined in the beginning of Chapter 5, is 

 the square of the path factor for one-way trans- 

 mission. Therefore the change with distance in the 

 received-field strength is more rapid with radar than 

 with the one-way radio. 



In order to study this relationship, two small 

 mobile radar sets on the S and X bands were set 

 up near the transmitter of the long path, at Province- 

 town. Echoes from natural targets along the coast 

 of the mainland were studied in connection with the 

 soundings and correlated with the one-way trans- 

 mission measurements. In Figure 8 is shown a 

 correlation between the signal strength of the X-band 

 radar and the signal strength of the high X-band 



o 



100 



< S 120 



t- 



S 



IE O 



< -I 

 1- UJ 



u. m 



° m 140 



1 ° 



I- 

 o 



160 



in 



100 80 60 40 



DB BELOW 1 WATT 

 SIGNAL STRENGTH 



20 



Figure 8. Correlation between one-way and radar sig- 

 nal strengths over the same path. X band, Massachu- 

 setts Bay. 



