Hameg HZ540 Benutzerhandbuch Seite 35

M e a s u r e m e n t o f S h i e l d i n g A t t e n u a t i o n o f S h i e l d e d H o u s i n g s
Next, the same measurement is performed with
the additional shielding around the EUT. Again the
EUT must be rotated in azimuth until the maximum
RFI is observed. The direction may be different
than in the non-shielded equipment.
EUT RFI Characteristics with Additional Shiel-
ding
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 effective-
ness 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 be-
cause the radiation may also occur from windows
and other openings in the housing or cables con-
nected to the EUT. However, it is cost-effective to
measure before spending money for sheet metal.
35
Subject to change without notice