Additional tests were conducted on a sub-set of devices to determine the field strength of these devices when they are operated in a vehicle. For this test, the device was installed as per normal operation in a vehicle. Then measurements were made of the field strength from the device at a distance of 3 m from the vehicle’s antenna (see Figs. 5 and 6). For this test, three “Wireless” devices were tested and two “Wired” devices were tested. The combined test results are shown in Table 5 and Fig. 7.
TABLE 5
“Car test” devices measurement results
Device
|
Frequency 1
|
Field strength
w/K factor (dBμV/m)
|
Frequency 2
|
Field strength
w/K factor (dBμV/m)
|
Frequency 3
|
Field strength
w/K factor (dBμV/m)
|
9
|
88.3
|
65.0
|
98.5
|
76.2
|
107.7
|
77.2
|
12
|
88.3
|
66.8
|
100.5
|
67.4
|
106.5
|
60.6
|
15
|
88.1
|
55.8
|
98.5
|
55.3
|
107.7
|
59.0
|
20
|
87.9
|
50.4
|
88.3
|
49.8
|
NA
|
NA
|
21
|
87.9
|
42.0
|
88.3
|
42.1
|
88.7
|
43.6
|
Figure 5
Setup for “Car test”
The results indicate that for the three “wireless” devices (No. 9, 12 and 15); they generally exceeded the prescribed 48 dBμV/m limit. Thus, the “attenuation” of the vehicle does reduce the field strength outside the vehicle by an average of approximately 11.2 dB. However, the devices are still well beyond the maximum permissible emissions.
The “wired” devices (20 and 21) were generally compliant (within a tolerance value of 1-2 dB), although the “attenuation” of the vehicle was not as significant of a factor, as leakage through the vehicle antenna was the main radiator. In this case, the “average” attenuation was 2.6 dB.
Figure 6
“Car test” setup
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