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LANGER
DE-01728 Bannewitz
mail@langer-emv.de
EMV-Technik
www.langer-emv.com
3.4 Reason analysis with near field probes
Carry out near-field measurements to exactly determine the RF sources that emit disturbances.
The goal is to correlate the currents measured with the RF current transformer to the RF fields on
the module. You should proceed as shown in Figure 20:
Figure 20 Field measurement with near-field probes
In each measurement you determine
- the field strength at a certain frequency or within a certain frequency range and
- the direction of the magnetic field lines by rotating the magnetic field probe (magnetic field
measurements).
The following fields should be considered as potential RF sources:
- electric fields above components such as processors
- electric fields on switched lines and bus systems
- magnetic fields on switched data and clock lines
- magnetic fields on power supply lines
Figure 21
Begin by determining the magnetic and electric
fields in the vicinity of the modules. These
fields incite the whole metal system of the unit
under test to oscillate (exciting fields) and must
finally be reduced. You should use near-field
probes with a bigger probe head, i.e. the probe
RF-R 400-1 for magnetic and the probe
RF-E 02 for electric fields.
These measurements give you an idea of the
respective disturbance emission mechanism.
As a next step, locate the sources of these
exciting fields. The probes with smaller probe
heads such as the RF-R 3-2 magnetic field
probe are particularly suitable for this job.
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ESA1
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