Overview
This topic explains the effects of electromagnetic interference (EMI) and radio frequency interference (RFI) from the switch on nearby devices such as radios, televisions, and telephones, and outlines guidelines to reduce EMI and RFI.
Electromagnetic interference (EMI) and radio frequency interference (RFI) from the switch can adversely affect other devices, such as radio and television (TV) receivers. Radio frequencies emitted by the switch can interfere with cordless and low-power telephones. RFI from high-power telephones can cause spurious characters to appear on the switch monitor.
RFI is defined as any EMI with a frequency above 10 kilohertz (kHz). This type of interference travels from the switch to other devices through the power cable and power source or through the air as transmitted radio waves. The Federal Communications Commission (FCC) publishes specific regulations to limit the amount of EMI and RFI that are emitted by computing equipment. These switches comply with FCC regulations.
Reduce the possibility of EMI and RFI by following these guidelines.
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Cover all open expansion slots with a blank filler plate.
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Always use shielded cables with metal connector shells for attaching peripherals to the switch.
When wires are run for any significant distance in an electromagnetic field, interference can occur to the signals on the wires with these implications.
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Improper wiring can result in radio interference emanating from the building's wiring.
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Strong EMI from lightning or radio transmitters can damage signal drivers and receivers in the chassis and create electrical hazards by sending power surges through lines into equipment.
To predict and prevent strong EMI, consult experts in radio frequency interference (RFI).
If you use a twisted-pair cable with a good distribution of grounding conductors, the wiring is unlikely to emit radio interference. Copper cables should not be longer than the maximum distances for the media type.
If the wire length exceeds the recommended distance, or if wires pass between buildings, consider the risks associated with lightning strikes. The electromagnetic pulse that is caused by lightning or other high-energy phenomena can easily couple enough energy into unshielded conductors to destroy electronic switches. Consult experts in electrical surge suppression and shielding if you have had similar problems in the past.