Measurement Of The Shielding Attenuation Of Shielded Housings With The E-Field Probe - Hameg Instruments HZ530 Manual Del Usuario

Measurement of the Shielding Attenuation of
Shielded Housings with the E-Field Probe
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not only at the time domain or a false picture may result. Theo-
retically, everything is contained in the time domain which is only
differently presented in the frequency domain. The problem rests
with the linear presentation and the resolution of the oscilloscope.
Using a generally poor oscilloscope will not lead to a theoretically
optimal solution.
What are the results if I surround the entire equipment in a shielded
housing? This question will be asked if I fail the CE-Mark EMC test.
Unfortunately, this question can not be answered in general because
a metallic housing is not always a good shield. No one wants to wait
until the next full-scale EMC test for the results. What if the EUT
fails again? What is needed is a simple measurement procedure
to determine the relative improvement of the radiated RFI. For this
purpose the highly sensitive E-Field probe is used, which is used
as broad bandwidth measurement antennas to help answer the
above questions.
First, before the E-field probe is used, determination must be made
if the probe has sufficient sensitivity and bandwidth. In general, all
passive probes are not usable since they have insufficient sensitivity.
The simplest solution to determine the sensitivity and bandwidth
is to measure the existing ambient field in the practitioner's labo-
ratory that is generated by the surrounding transmitters from 0
to 1,000MHz. Figure 8 shows the result of such a measurement
which was made with the active E-field probe from the HZ530 probe
kit connected to a spectrum analyzer. From 0 to 50MHz, Figure 8
shows relative high levels which originate from transmitters in the
broadcast band and shortwave region. In the frequency range near
100MHz signals from FM stations are noticeable. Since in the par-
ticular case measured, there were no nearby FM transmitters, the
amplitudes are relatively low. The strongest signal observed was
a UHF TV transmitter at 474 MHz which was located only 15 km
from the laboratory. Then up to 800 MHz are several weaker (more
distant) UHF TV transmitters. The final signals occur above 900MHz
which are related to cellular telephones. This data shows that the
probe is wideband and has sufficient sensitivity. From the AM band
around 1MHz to the cellular telephone band there are spectrum
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