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Chapter 11 - Electromagnetic Interference Measurement
106 V3.2
11.3
Antenna selection
The field strength that is displayed is acquired by measuring the antenna voltage and converting it,
taking into consideration the physical properties of the antenna used. The antenna being used can
be set under
ANTENNA
. Types EMI 240 and EMI 241 are currently supported.
A pre-amplifier is already integrated in the EMI 241 antenna. For the EMI 240/Y antenna, note, that
the correct measuring results will be obtained only in connection with the EMI 240/V pre-amplifier.
User-defined EMI antenna
11.3.1
In addition a user-defined antenna may also be defined. Enter the name and correction factor for
the EMI antenna using the menu item
EMIANT
.
Use the
↑/↓
arrow keys to choose between name and factor or select the
→
arrow key to access the
respective editing menu. Press
ENTER
to complete the entry.
Figure 11-2 EMI user-defined antenna
The edited name of the user-defined antenna is also applied for the corresponding menu item in
the
ANTENNA
menu. The correction factor that is entered governs the conversion of the level
measured by the receiver (in dBµV) to the displayed field strength (in dBµV/m). The following
relationship applies: E[dBµV/m] = L[dBµV/m] + Factor[dB].
11.4
Entering the distance
The limits for observing the EMI are based on the norm-distance of 3m to the outer wall of the
building. As it is not always possible to take a measurement from 3m away, the interference field
strength at a greater distance can be measured and converted to the reference spacing of 3m
based on the current spacing to the building. The measuring instrument requires the distance to be
entered for the conversion.
The measured distance can be entered under
DISTANCE
. This can be determined easily with the
help of the additionally available DLE 70 laser distance measuring device, which can be mounted
to the EMI 240/Y antenna.
11.5
Entering the limit
There are official regulations for observing the interference radiation of cable systems. They set
limits for the emission field strength at a distance of 3 m. The maximum field strength can be
entered into the instrument. The instrument uses it for certain warnings when the limit has been
exceeded. The maximum field strength in dBμV/m can be entered with the
LIMIT
button.