Radio and Television Interference Noise See Also: Corona, Interference, Radio Frequency Interference - Neas Letter Electromagnetic Field(s) interference from overhead Power lines is caused by two phenomena; complete electrical discharges across small gaps (microsparks) and partial electrical discharges (corona). Gap-type sources occur at Insulators, line hardware, and defective equipment and are a construction and maintenance problem rather than a design consideration. They are responsible for about 90 percent (see Standard Handbook for Electrical Engineers - see Engineer - You Might Be One If ... , page 14-13) and can be located and eliminated as they occur. Conductor and hardware corona Noise rarely results in complaints except perhaps in weak Television and/or Radio signal areas. In the few cases whe re corona-caused television noise has occurred in foul weather, it has often been possible to fix the problem by an improvement in the receiving Antennas rather than changes to the transmission line design. The specification of corona-free hardware can be important to eliminate that source of electromagnetic interference and is especially important as lines are constructed with closer spacing (due to continued residential development) and resulting higher Electric Fields on the hardware. Conductor clamps and other fittings which were formerly acceptable at traditional phase spacing may not be adequate for compact lines. For Alternating Current (AC) lines, radio and television noise are functions of weather. Fair-weather noise may be significant and varies with the season, Wind velocity, and barometric Pressure.