30 TECHNICAL SURVEY 
Taste 1. S and X bands, July and August. 
Per cent of Percent of Per cent of 
time above _ time below time 
Date standard standard standard 
July 10-16 63 36 1 
Aug. 21-27 97 3 0 
Aug. 28-Sept. 3 80 15 5 
TaBLE 2. Sand X bands, September and October. 
Per cent of Percent of Per cent of 
time above _ time below time 
Date standard standard standard 
Sept. 25-Oct. 1 Ss 58 15 27 
x 80 10 16 
Oct. 16-22 S 76 2 22 
XK 92 0 8 
high and low receivers are closely parallel, Figures 5 
and 6 show these correlations graphically; the first is 
between the S and X bands and the second is between 
the high and the low 8-band receivers. In contradis- 
tinction there is practically no correlation between 
RECEIVERS 
HIGH ae SEPT 18-24 1944 
X BAND 
DB BELOW 4 WATT 
110 
100 80 60 40 20 
DB BELOW 41 WATT 
S BAND 
FicureE 5. Correlation between S- and X. 
strengths, Massachusetts Bay. 
<-band signal 
LOW RECEIVER 
DB BELOW 1 WATT 
eee or | | 
cibeeeele 
100 
ee eae 1 oe 
HIGH RECEIVER 
Ficure 6. Correlation between signal strengths at high 
and low receivers, Massachusetts Bay. 
HIGH SEPT 18-24 1944 
RECEIVERS G 
117 MC 
e OB BELOW 1 WATT 
100 80 60 40 20 
DB BELOW 1 WATT 
S BAND 
Figure 7. Correlation between 117-me and S-band sig- 
nal strengths, Massachusetts Bay. 
the S-band and 117-mce 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 occut 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 1, 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 trams- 
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 
receiver of the long transmission path. The radar 
target is near the one-way receiver so that both paths 
are practically coincident. When the radar signal was 
below the limit of sensitivity, it is indicated on the 
eraph by this limit so that the lower points of the 
diagram really have little physical significance. If a 
straight line is drawn, averaging the variation of the 
higher points, its slope is roughly 2:1 as should be 
expected. 
Figure 9 shows a correlation between the one-way 
signal strength on the S band and the maximum 
range of fixed echoes detected by the S-band radar 
along the coast. It is interesting to note that super- 
standard radar ranges do not appear until the one- 
way signal has reached a certain, rather larger value. 
