NEC nd-20292 manual Nformation

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 Mark11is a digital communications system, and under normal conditions is immune to radio frequency interference. However, in areas with very strong RF1fields, the Electra Mark11may be affected. This Engineering Technical Information (ET11Bulletin 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

2.1AC 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 RF11from coupling RF1to the Electra Mark11system via the AC wiring.

2.2OTHER 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 RF1to 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 Mark11system, 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.

2.3UNUSED 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 Mark11system. In some instances, RF1 may be introduced into the system at more than one place. The major areas in the Electra Mark11to be investigated, to locate RF1input, are:

Station handset Station line cord

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