Information

EMI Pre-Compliance Guide RIGOL Technologies
RIGOL Technologies CO., LTD. 09.09.2021
Figure 11: First overview of DUT interferences with near field probing
Tests on housing leakage could be detected as well as strong disturbance components like
ribbon cables or LCD panels. Bigger probes are usable to find the area of interferences.
Smaller probes can be used to detect the exact source.
One approach for near field analysis is to use the spectrum analyzer with linear frequency
scale / no limit lines and test e.g. a frequency range of 30 MHz to 500 MHz with a RBW of 100
kHz and activation of pre-amplifier (internal attenuator: 0 dB) to get a first view the
interference peaks of DUT (see figure 11).
Radiated Emission
According to the description at the beginning, propagation starts when λ is small to the
geometry and E & H are no longer independent. Both are in-phase and propagate to the
environment. Radiated emission is not easy to test. In a test laboratory a big hermetic test
chamber is used where far field conditions are fulfilled and other influences (due to external
components like a mobile phone, etc.) are not visible in the result. Far field condition starts
with a distance of 4 * λ and the characteristic wave impedance is 120 * π Ω (= 377 Ω). The
hermetic room has in most cases at the wall broadband absorber for impedance matching of
EM wave to avoid reflections. The altitude of broad band antenna can be changed during a
test to find the highest peak at DUT during the test
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Because of „2 way propagation“ with direct beam and one reflection point on earth