The problem of power line noise interference with AM radio broadcasting systems has been an issue ever since radio broadcasts began, because it disrupts proper antenna impedance matching between a transmission line and AM wave radio towers. Power line noise can affect everything from radio and television reception to amateur radio, as well as communications from police, the military, and firefighters.
This discussion will consider how and why the problem occurs, and what can be done to mitigate or eliminate its effect on radio broadcasts and users of electronic devices.
How Power Line Noise Originates
Almost all power line noise originates from equipment used by utility companies, and is created as arcing occurs between any two conductors in power line hardware. The gaps which electricity can spark across are most often attributable to loose hardware, or hardware that was improperly installed. A typical example would be inadequate spacing between a ground wire and a staple.
Tracking Down the Source Problem
The quickest and most cost-effective way to locate and correct a problem with power line noise is to engage the services of an interference investigator. Since the problem has been around for decades, an entire industry has grown up around how to combat the issue, and proven techniques have evolved over time to quickly zero in on the source of any problem.
The process will generally include some combination of the following procedures. First of all, it is necessary to eliminate the possibility that the interference is actually originating in the broadcaster’s own building. As many as half of all interference complaints filed do originate in the same building occupied by the complainant.
One of the key steps in an investigation is to monitor the complainant’s equipment while the interference problem is still active, and this is true whether the problem is television interference or radio frequency interference. Assuming the problem is determined to be a source external to the complainant’s building, the next step an investigator would take is to attach a Defect Direction Finder (DDF) receiver to the building’s antenna. This allows the investigator to monitor the sound and patterns produced by interference sources as they are received through the building’s antenna.
Matching Power Line Noise Patterns
The pattern of interference detected by the DDF receiver is a kind of signature for the power line noise, and it can be matched against readings taken out in the field to narrow down the source of the problem. Any power line noise problem external to the complainant’s building will always have a matching signature among potential sources out in the field.
Readings taken out in the field should follow a logical and systematic approach which begins at the complainant’s building. From there it should gradually broaden out in circles moving away from that building, until a pattern is received which matches the pattern detected at the complainant’s building.
Pinpointing the Problem
Once the source of the interference has been pinpointed to a specific building, all that remains is to identify the equipment which is causing the problem. Investigators will use a hot stick mounted locator or an ultrasonic dish to help pinpoint the source of an arc which would be causing the interference.
Some of the most common offenders are loose staples on ground conductors, a ground conductor touching nearby hardware, a guy wire touching a neutral, loose hardware, a bare tie wire used with an insulated conductor, loose cross arm braces, and sometimes even lightning arrestors.