R&S MDS-21
Operation of the Absorbing Clamp
User Manual 1142.8407.04 - 02
E-12
A ferrite absorber in the MDS absorbing clamp surrounds the power cable and acts as
resistance for the high-frequency RFI power. The incoming current is measured at the
absorber input using a current transformer and an EMI measuring receiver. Since there
is no matching between the disturbance source, the cable and the absorber in this
setup, the MDS absorbing clamp is slid along the cable to find the maximum current.
● The spacer for centering test cables with a diameter less than 6 mm has to be
removed for measuring EUTs with a test cable whose diameter exceeds 6 mm.
The spacer increases the measurement accuracy for thin cables (e.g. for
calibration).
● For measurements, close the absorbing clamp with both eccentric catches.
● The current transformer must point towards the EUT. This side of the absorbing
clamp is
marked with “EUT”.
● Move the absorbing clamp away from the EUT until the greatest deflection is
obtained on the receiver indicator. The person who is moving the clamp holds the
clamp on the side facing away from the EUT. In the case of a permanent
installation, it is recommended to use a pull cord to move the clamp along the non-
metallic guiding tracks.
● In principle, the first maximum value observed when moving away from the EUT
ought to be measured. At frequencies above 150 MHz, the second maximum value
or the position closer to the EUT may provide higher results.
Read the disturbance power on the measuring receiver:
Measured
disturbance power
dB (pW)
=
Voltage
reading
dB (µV)
+
Clamp factor
(calibration)
dB (pW/µV)
The clamp factor can be found in the supplied calibration protocol.
