Hameg Instruments HZ530 Manual Del Usuario página 43

until the maximum RFI is observed. The direction may be different
than in the non-shielded equipment.
EUT RFI
Characteristics
with the
Additional Shielding
Figure 10
Figure 10 shows the data with the additional shield. By comparing
Figure 10 with Figure 9, it is observed that the entire spectrum is
lower. The shielding attenuation can be determined from these two
figures. For the marker frequency of 275MHz a signal of -55.9 dBm
gives a shielding effectiveness of [-42.8(-)-55.9 dBm] of 13.1 dB.
For the frequency of 800MHz, the shielding effectiveness is only 9
dB. Shielding effectiveness of this magnitude are hardly worth the
additional sheet metal. But such results are quite common. These
measurements were performed on an EUT which was low-price
frequency counter. There is other equipment where similar results
are obtained because the radiation may also occur from windows
and other openings in the housing or cables connected to the EUT.
However, it is cost-effective to measure before spending money
for sheet metal.
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