Chapter 11 - Electromagnetic Interference Measurement
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106 V3.2
11.6
Analysis of identifier
The electromagnetic interference measurement is based on using the KFG 242 frequency
identification generator. This generator is used as a defined source of interference in a cable
system and should be integrated into the head end.
The signal of the interference transmitter is modulated with an identifier for the unique assignment
of the interference emission. This can be programmed in the frequency identification generator as
text with up to 13 characters.
The measuring instrument demodulates the identifier and shows it in the top row on the display. To
demonstrate that the identifier is being received continuously, the instrument clears the text and
shows it again.
11.7
Measuring the interference field strength
Figure 11-3 EMI measure field strength
When tuned to a frequency, the instrument measures the antenna voltage of the receiving antenna
and converts it into the equivalent field strength. The absolute field strength is displayed in dBµV/m
in a larger font. The measuring range is from 3 – 103 dBµV/m (EMI 241) or 5 – 105 dBµV/m (EMI
240) with a resolution of 0,1 dBµV/m.
At the same time, the instrument calculates, in connection with the current spacing, reference field
strength at a distance of 3 m to the building and displays it in a smaller font in the row above the
menu bar. If the reference field strength exceeds the set limit, a warning message will appear on
the display. A warning signal sounds at the same time over the loudspeaker.
11.8
Setting the identifier
The measuring instrument has a help setting for setting the identifier of the frequency identification
generator. Application note “AN002 – Measuring electromagnetic interference” contains information
on how to set and change the identifier for KFG 242.
If a character received from the identifier is marked showing that this character is one that can be
changed with two buttons on KFG 242, this character will be displayed inverted on the display. If no
character is displayed inverted (normal mode), it means that there is no character that is currently
selected for modification.