Electrical Noise/Radio-Frequency Interference - AT&T MERLIN LEGEND Release 3.1 System Planning Manual

Confirming the Location of the Control Unit

Electrical Noise/Radio-Frequency Interference

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.
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Before You Begin