Two noise sources are likely to cause interference with a ham radio: electric and electronic. Electric noise is caused primarily by arcing in power lines or equipment, such as motors, heaters, and electric fences. Electronic noise is caused by leaking RF signals from consumer appliances and computers operating nearby. Each type has a distinctive signature, or characteristic sound. The following list describes the signatures of common sources of electric noise:
Power line: Steady or intermittent buzzing at 60 Hz or 120 Hz. The weather may affect interference.
Power-line noise is caused by arcing or corona discharge. Arcing can occur around or even inside cracked or dirty insulators. It can also occur when two wires, such as neutral and ground wires, rub together.
Corona discharge occurs at high-voltage points on sharp objects where the air molecules become ionized and electricity leaks into the atmosphere. The interference is a 120 Hz buzzing noise because the arc or discharge occurs at the peaks of the 60 Hz voltage, which occur twice per cycle.
Do not attempt to fix problems with power lines or power poles. Always call your power company.
You can assist the power company by locating the faulty equipment. You can track down the noise source with a battery-powered AM radio or VHF/UHF handheld radio with an AM mode (aircraft band works well). If you have a rotatable antenna at home, use it to pinpoint the direction of the noise. (The null off the side of a beam antenna is sharper than the peak of the pattern.)
Walk or drive along the power lines in that direction to see whether you can find a location where the noise peaks. You can find power poles with bad hardware by driving around with the car’s AM radio tuned between stations.
If you do find a suspect pole, write down any identifying numbers on the pole. Several numbers for the different companies that use the pole may be on it; write them all down. Contact your utility and ask to report interference. You can find a great deal more information about this process on the ARRL RFI web page.
Industrial equipment: Sounds like power-line noise but with a more regular pattern, such as motors or heaters that operate on a cycle. Examples in the home include vacuum cleaners, furnace fans, and sewing machines.
Defective contacts: Highly erratic buzzes and rasps, emitted by failing thermostats or switches carrying heavy loads. These problems are significant fire hazards in the home, and you need to fix them immediately.
Dimmers and speed controls: Low-level noise like power lines that comes and goes as you use lights or motors.
Vehicle ignition noise: Buzzing that varies with engine speed, which is caused by arcing in the ignition system.
Electric fences: Regular pop-pop-pop noises at about 1-second intervals. A defective charger can cause these problems, but the noise is usually due to broken or missing insulators or arcing from the fence wires to weeds, brush, or ground.
Finding an in-home source of electric noise depends on whether the device is in your home or a neighbor’s. Tracking down in-home sources can be as simple as recognizing the pattern when the noise is present and recognizing it as the pattern of use for an appliance.
You can also turn off your home’s circuit breakers one at a time to find the circuit powering the device. Then check each device on that circuit.
If the noise is coming from outside your home, you have to identify the direction and then start walking or driving with a portable receiver. Review the ARRL RFI website or reference texts for information about how to proceed when the interfering device is on someone else’s property.
What about electronic noise? The following list describes the signatures of common sources of electronic noise:
Computers, videogame consoles, and networks: These devices produce steady or warbling tones on a single frequency that are strongest on HF, but you can also hear them at VHF and UHF.
Cable and power-line modems: You hear steady or warbling tones or hissing/rasping on the HF bands.
Cable TV leakage: Cable TV signal leakage at VHF and UHF sounds like a buzzing (video signal) or audio FM signal with program content. Cable channel 12 covers the same frequencies as the 2 meter band, for example. Cable TV systems are converting to digital signals that just sound like hissing noise.
Plasma TVs: Although a few models are RF-quiet, many generate noise across a wide spectrum of frequencies. The only solution seems to be to replace them with LCD or LED models, which don’t have the noise problem.
Each type of electronic interference calls for its own set of techniques for finding the source and stopping the unwanted transmission. You’re most likely to receive interference from devices in your own home or close by because the signals are weak. If you’re sure that the source isn’t on your property, you need a portable receiver that can hear the interfering signal.
The ARRL RFI website has some helpful hints on each type of interference, as well as guidance on how to diplomatically address the problem (because it’s not your device). The webOverview page of the ARRL RFI website contains excellent material on dealing with and managing interference complaints (both by you and from others). ARRL members have access to the league’s technical coordinators and technical information services.
You can eliminate or reduce most types of interference to insignificant levels with careful investigative work and application of the proper interference-suppression techniques. The important thing is to keep frustration in check and work the problem through.