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MERLIN LEGEND Communications System Release 6.1
Installation
555-661-140
Issue 1
August 1998
Installing the Control Unit
Page 2-3
Overview
!
WARNING:
Do not install the control unit outdoors.
Electrical Noise/Radio-Frequency Interference
In most cases, electrical noise is introduced into the system through
trunk or telephone cables. However, electromagnetic fields near the
control unit can also cause noise in the system. Therefore, you should
not
place the control unit and cable runs 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 radio-frequency
interference (RFI). Small tools with universal motors are generally not a
problem when they operate 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. To estimate the field strength produced by radio
transmitters, divide the square root (√) of the emitted power, in kilowatts,
(÷) by the distance from the antenna in kilometers which equals (=) the
field strength in volts per meter.
Example: √49,000 kw
= 7,000 ÷ 10 km (6.2 miles) = 0.7 volts per
meter
This yields the approximate field strength in volts per meter and is
relatively accurate for distances greater than about half a wavelength
(492 ft., or 150 m, for a frequency of 1000 Hz). If the result exceeds 1.0
volt per meter, you may have to install shielded cables and/or Z200A
filters. See Appendix A, “Customer Support Information,” following
Maintenance and Troubleshooting,
for FCC Part 15 radio frequency
regulations.