user manual

NEC AMERICA, INC.
BUSINESS SYSTEMS DIVISION
NFORMATION
ET1 NUMBER: MK-006
DATE: FEBRUARY, 1998
LOCATING AND ELIMINATING RADIO FREQUENCY
INTERFERENCE (RFI) ON ELECTRA MARK11 INSTALLATIONS
1.
DESCRIPTION
The Electra Mark11 is a digital communications system, and under normal conditions is immune to radio
frequency interference. However, in areas with very strong RF1 fields, the Electra Mark11 may be affected.
This Engineering Technical Information (ET11 Bulletin describes the steps necessary to eliminate radio
frequency interference. This modification procedure should be implemented only to the portion of the
system experiencing RFI.
2.
INSTALLATION CONSIDERATIONS
2.1
2.2
2.3
AC GROUNDING The AC circuit used to power the Electra MarkII system must be a dedicated
circuit with a ground provided through the AC outlet wiring, back to the main entrance power.panel.
This method of grounding prevents certain types of equipment (such as arc welders, which may
generate RF11 from coupling RF1 to the Electra Mark11 system via the AC wiring.
OTHER GROUND: If a suitable ground is not available at the AC outlet, an earth ground rod or cold
water pipe ground must be used. This ground must be connected to the ground lug provided on the
ESE-32B-1 CCU via l2AWG wire, minimum. When using a cold water pipe for ground, ensure that
the water pipe is providing earth ground.
If the water pipe is not common to earth ground, it may act
as an antenna, coupling RF1 to the system.
If there is any doubt about the available ground, an earth
ground rod should be installed in accordance with local Telephone Operating Company procedures,
Grounding the Electra Mark11 system, to both AC circuit ground and cold water pipe ground or a
ground rod, may cause a ground loop, leading to sporadic system operation if the two grounds are at
different potentials. Multiple ground connections are not recommended.
UNUSED WIRE PAIRS: Any unused wire pairs in the station cables (and the 25 pair J cable) should
be connected to a confirmed earth ground, at the MDF side. Grounding the spare wires (in the station
cable) at both ends of the cable run may cause the spare wires to act as an antenna, if the two grounds
are at different potentials, and is therefore not recommended.
3.
LOCATING THE RF1 SOURCE:
Prevailing conditions at each site are rarely the same, therefore, there are no specific guide lines to follow in
locating RFI sources. The primary task is to identify the area(s) where RF1 is being induced to the Electra
Mark11 system. In some instances, RF1 may be introduced into the system at more than one place. The
major areas in the Electra Mark11 to be investigated, to locate RF1 input, are:
Station handset
Station line cord
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