SI-3C
™
U
ser
’s M
anual
27
(0) degrees is preferable, because the displayed speed is the actual
target speed . However, in all uses of police radar, the radar device is
always at a slight angle to the target vehicle to avoid collisions .
Velocity
Vector
Angle
Radar
Figure 5.2.1
An angle between the antenna and the
target causes the cosine effect
The following table shows the effect that an increasing angle has
on a displayed speed .
Horizontal Angle Degrees
Actual
Speed
0° 1° 3° 5° 10° 15° 20° 30° 45° 60° 90°
Displayed speed:
30 mph
30 29 29 29 29
28
28
26
21 15
0
40 mph
40 39 39 39 39
38
37
34
28 20
0
50 mph
50 49 49 49 49
48
46
43
35 25
0
60 mph
60 59 59 59 59
57
56
51
31 30
0
70 mph
70 69 69 69 68
67
65
60
49 35
0
80 mph
80 79 79 79 78
77
75
69
57 40
0
Table 5.2.1
Actual and displayed speeds at antenna-to-target angles
Small angles (less than 10°) have little effect on accuracy . As the
angle increases, the displayed speed decreases . At 90°, the target
speed is 0—grossly incorrect .
