10 



TRANSMISSION EXPERIMENTS OVER MASSACHUSETTS BAY 



Figure 5 shows the relation between S-baiid signal 

 strengths for high and low receivers; the correlation 

 is excellent in practically every case. A similar cor- 

 relation exists for the high and low X-band signal, 



20 



40 



< 

 S§60 



'^ QJ 



m 



m 



80 



110 



100 80 60 40 



DB BELOW 1 WATT 

 S BAND 



20 



Figure 4. Relation between S- and X-band signal 

 strengths. 



except for the case of \ory low signal where the ap- 

 parent average vahie of the signal strength on the 

 low reeeixer is alwavs relativelv high. Whether this 



40i 



"=0 80 

 om 



o 



100 



120 



100 80 60 40 



OB BELOW IWATT 

 HIGH RECEIVER 



20 



FiGUKE .5. Relation between signal strengths at high 

 and low receivers. 



is caused by tlie lack of receiver sensitivity or is a 

 real transmission phenomenon cannot be conclusively 

 decided on the basis of the present information. 



Figure 6 shows the relation of signal strengths at 

 117 mc and S band; the difference between this figure 

 and the preceding two speaks for itself. From the pre- 

 liminary analysis no consistent correlation has been 



found between the beluivior of the low- 

 frequency transmission. 



and hiu'h- 



100 



o 



"0 120 

 m 



a 



1401 



100 80 60 40 



DB BELOW 1 WATT 

 S BAND 



20 



Figure 6. Relation between 117-mc and S-band signal 

 strengths. 



The \ariations on the two paths are generally in 

 good agreement although changes in signal type rare- 

 ly occurred exactly simultaneously; the changes on 

 the short path are always less in magnitude than ou 

 tlie other, as would be expected. 



As far as can be determined from the available 

 data the K-band signal correlates quite well in gen- 

 eral with that on S and X bands. Only high signal 

 can he observed, of course, with the present equip- 

 ment. 



I^HLATION OF EaDIO RusULTS TO MODIFIED 

 lXDi:X CUKVES 



Detailed conclusions must await Ihe full analysis 

 ol' the data. At present certain qualitative conclu- 

 sions can be drawn : 



1. When the surface modified index inversions are 

 present, the microwave signal level is high on the 

 average, and usually the signal has roller-type fades. 



3. When the M curve is substandard the signal is 

 low and scintillating. The M curves which are stand- 

 ard all the way down to the surface of the water 

 appear to be very rare, even when the air is colder 

 than the water. The previous results on the short 

 path had tended to discount the importance of the 

 low il/ inversions which exist over water most of the 

 time, especially with cold air flowing out from the 

 land. The increased sensitivity of the present setup 

 to variations in the M curve, the additional jDath 

 length, and finally the inclusion of the X-band trans- 

 mission on the circuit have shown definitely that such 

 low M inversions are far from negligible but will 

 affect S-1)and conununications (or one-way trans- 



