96 TECHNICAL SURVEY 
TABLE 2. Type SCR-270B. Characteristics of antenna 
pattern. 
Horizontal pol. Vertical pol. 
Half-power beam angle 26° 6.5° 
First null angle 40° 14° 
Secondary lobe angle 45° ae seed 
Secondary null angle 90° 
Secondary lobe angle 5% 
Back radiation 4% 
Other characteristics of this set are as féllows: 
Pulse width 30 usec = 3 miles 
Nominal range 150 miles 
Sweep sector 185° to 290° 
Elevation: center of antenna 387 ft 
From these data may be calculated the relative 
echo strengths of mountains at various distances 
and the relative side and back echoes. A reference 
SS 
Zs 
SCALE 1:1,000,000- 
CONTOUR INTERVAL 1000 FEET 
value of 1.0 is taken for the main echo from a typical: 
mountain 100 miles distant, and the relative intensity 
from Figure 40 is taken equal to 1.0. It is estimated 
that all echoes whose strength compared to the 
reference value is over 0.25 will be strong enough to 
obscure targets. Thus the back echo of a mountain 
10 miles away in a diffraction region where the 
relative strength is 0.5 would have an echo value 
of (100/10)? K 0.5 x 0.04 = 2.0 and should be 
plotted since it exceeds 0.25. 
A table may be constructed for the main, side, 
and back lobes (M, S, B) for various distances and 
degrees of diffraction to show which echoes should 
be plotted. Table 3 is such a table, corresponding to 
a reference strength equal to 0.25. This table will 
apply only for the conditions of this example. 
In Figure 42 is shown a topographical map of the 
Fiaure 42. Topographical map for Example 8. 
