AT&T 3.0 manual Electrical Noise/Radio-Frequency Interference, Control Unit Requirements

Overview

Electrical Noise/Radio-Frequency Interference

In most cases, electrical noise is introduced to 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,” followingMaintenance and Troubleshooting, for FCC Part 15 radio frequency regulations.

Control Unit Requirements

■Dimensions

—Basic carrier: 14 in. wide by 23 in. high by 12 in. deep

—Basic carrier and one expansion carrier: 25 in. wide by 23 in. high by 12 in. deep

Installing the Control Unit 2-3