Lucent Technologies 6.1 manual Electrical Noise/Radio-Frequency Interference

MERLIN LEGENDCommunications System Release 6.1		Issue 1
System Planning 555-661-112		August 1998
1 Before You Begin
	Confirming the Location of the Control Unit	Page 1-5
	Electrical Noise/Radio-Frequency Interference	1

In most cases, electrical noise is introduced to the system through lines/trunks or telephone cables. However, electromagnetic fields near the control unit may also induce noise in the system. Therefore, the control unit and cable runs should not be placed in areas where a high electromagnetic field strength exists. Radio transmitters (AM and FM), television stations, induction heaters, motors (with commutators) of 0.25 horsepower (200 watts) or greater, and similar equipment are leading causes of interference. Small tools with universal motors do not generally cause a problem when operated on separate power lines. Motors without commutators generally do not cause interference.

Field strengths below 1.0 volt per meter are unlikely to cause interference. Estimate the field strength produced by radio transmitters by dividing the square root of the emitted power (in kilowatts) by the distance from the antenna in kilometers.

This yields the approximate field strength in volts per meter and is relatively accurate for distances greater than about half a wavelength (492 feet, or 150 m, for a frequency of 1000 Hz).

To comply with FCC Part 15 requirements, each power supply on a newly installed system must have a ferrite core installed around the AC power cord and ground wire. Beginning with Release 2.1 this ferrite core is packaged with the power supply module at the factory. Ferrite cores are also compatible with earlier releases.