PKorAGATlON STUDIES AT MICKOW AVE FI11:qUENCIES 



97 



On the 11:44 picture there is just a trace of ii second pulse. Tlic next 

 set of pictures (Fig;, (i) were taken a little over an hour later on the same 

 nij;ht and show about the same conditions, that is, pulse amplitude and 

 shape change and other evidence of the presence of a second pulse delayed 

 alxmt 2 to 3 millimicroseconds. 



On the night of ()ctoh(n- l2, fading, which was apparently due to ti'ans- 

 mission by way of two paths with little path difference, was observed. 

 Some of the results are shown on Fig. 7. At 7:49 two distinct pulses are 

 evitlent, there l)eing (i millimicroseconds btMween tiieir peaks. One might 

 conclude from this that there was a scM'ond path about (> feet longei' than 

 the main path but the total lengtli of the disturbance along the base line 

 and the shapes of the pulses imhcate that the actual path difference was 

 about 2 to :3 feet. 



Apparently we had here two pulses of r-f energy overlapping in time 

 and in\()l\ing a large number of fre(iiiencies. These pulses are capable 

 of interfering with each other in a rather complicated manner, it being 

 possible for some fre([uencies tt) add and others to cancel at the same time, 

 depending upon their relative phases. Phase relationships of course de- 

 pend upon freciuency and path length differences. As a result pulses may 

 be distorted and ha\'e their peaks shifted about by a considerable amoimt. 

 We must, therefore, realize that the first pietiu'e of Fig. 7 does not really 

 represent two distinct pulses as appears to be the case, but actually shows 

 the resultant interference pattern of two o\'erlapping pulses. Since 

 a change of path difference of only about one and one-half inches is 

 enough to produce a 180° change in relati\'e phase at 4000 mc, it is not 



I'ig. 6 — Received pulses (list urhed t lansinission 



