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I. Introduction (By Mike Gruber, ARRL Laboratory)
 FCC Part 15 rules require that utilities and other operators of "incidental radiators," such as power lines, cause no harmful interference to licensed operations |
Although the problem has been around since the dawn of radio communications and broadcasting, power-line noise is on the rise. The proliferation of electrical and electronic devices that are potential victims of power-line noise, coupled with today's increased dependence on mobile and wireless communications, have each contributed to this increase. Dealing with a power-line noise complaint does not have to be time consuming or expensive -- and it's the law! A little knowledge can go a long way toward avoiding a fine from the FCC.
Power-line noise can interfere with radio communications and broadcasting. Essentially, the power-lines or associated hardware improperly generate unwanted radio signals that override or compete with desired radio signals. Power-line noise can impact radio and television reception -- including cable TV head-end pick-up and Internet service. Disruption of radio communications, such as amateur radio, can also occur. Loss of critical communications, such as police, fire, military and other similar users of the radio spectrum can result in even more serious consequences.
Let's now take a look at power-line noise, and how to best
handle a complaint in a timely and economic fashion.
 Fig1. "Bell" insulators are often the cause of RFI noise. The problem is most often associated with corrosion in a joint, as shown by this photo. |
 Fig 2. Arcing occurred between two of the three components in this insulator. It was significant source of noise until it was replaced by utility personnel. |
The Cause of Power-Line Noise
Virtually all power-line noise, originating from utility company equipment, is caused by a spark or arcing across some power-line related hardware. A breakdown and ionization of air occurs, and current flows between two conductors in a gap. The gap may be caused by broken, improperly installed or loose hardware. Typical culprits include insufficient and inadequate hardware spacing such as a gap between a ground wire and a staple. See Figures 1 and 2. We'll be discussing more specific causes of power-line noise in a later section.
Note: The terms "gap" and "conductors" should be interpreted broadly in this case. While not a source of power-line noise, a gap can exist in the commutator of a motor. A gap can also exist between insulator units and other parts of a utility structure. In some cases, the "conductor" can be the wood on the utility pole.
A brief mention should be made concerning corona. Contrary to a common misconception, corona discharge is rarely, if ever, a source of power-line noise. Corona discharge is defined as the partial breakdown of the air that surrounds an electrical element such as a conductor, hardware or insulator. In reality it is typically nothing more than a minor annoyance, as the noise caused by it is usually confined to lower frequencies. This noise does not propagate very far from the source because it is a low-current phenomenon that does not couple into the adjacent wires.
You've Received A Complaint -- What Next?
You've received a power-line noise complaint and investigated it. Based on your investigation, you've now concluded the problem is truly power-line noise. What next? The good news is locating and correcting most power-line noise sources is not particularly difficult or expensive. Proper training and equipment can make most cases a real snap. Let's now explore some of the best ways to handle these types of complaints -- from dealing with the customer to finding and fixing the noise source.
First, let's examine the fundamental issue of why we should care about a radio or television interference complaint in the first place. After all, aren't most utility lines and hardware associated with this type of complaint delivering electric power as they are intended?
