Interference Definitions and Causes

It may seem somewhat academic at this point to define interference but the bestunderstanding starts with a strong foundation in fundamentals.

Webster defines interference as: "4. radio.
a. A jumbling of radio signals, caused by the reception of undesiredones.
b. The signals or devices producing the incoherence.

Meanwhile the Federal Communications Commission (FCC) defines harmful interference asinterference which endangers the functioning of a radionavigation service or other safetyservices or seriously degrades, obstructs or repeatedly interrupts a radio communicationservice operating in accordance with the Radio Regulations.

From the amateur's standpoint, this means you cannot communicate. However, rememberthat the amateur service is not a safety or essential service, some moderation must beconsidered. e.g. hearing a distant co-channel repeater when your local repeater is notactive, while being annoying, is not "interference". Hearing adjacent channelsplatter while carrying on a conversation on simplex or your local repeater whileaffecting the quality of the conversation is not truly interference. If it makescommunication completely impossible then it should be considered interference although itstill may not be harmful or necessarily willful. Take note at this point, that many ofthe noise sources to be defined below do not affect FM/PM type radio operation except tocause desensing of the radio possibly masking the desiredsignal.

Taking Webster quite literally, we first examine types of interference:

  1. Non-Radio
    1. Electric Power sources: these mostly emanate from leaky insulators or cables belonging to the power company and with sufficient coaxing, they will repair them. It may take considerable convincing on your part but, once convinced they will repair them.
    2. Neon signs: These are more difficult to control because of their design. Most sign companies will not be cooperative, however the saving thing here is these typically do not interfere with FM/PM unless you are in the immediate proximity.
    3. Florescent Light fixtures: These when working properly are not a problem. However, when they fail, they can become annoying. If they fail, the alternatives are repair or replacement. In that same vein are the mercury vapor and sodium vapor lights used for outdoor lighting. These utilize an arcing mechanism for startup and when they fail, this becomes a great noise annoyance.
    4. Computer clocks etc.: This is a problem that is very pervasive with the increased appearance of faster and faster computers. Here, the best defense is Tempest shielded machines however these are not available for everyone especially your neighbor. An alternative is start with shielded/filtered power cords. On plastic cabinet computers, the use of RFI sprays on the interior of the case with conductive fingers to the metal chassis has been shown effective.. Monitors because of the harmonic rich signals that float around inside require special attention including RFI sprays, conductive fingers, filtered/shielded cables.

The biggest thing is don't let these problems beat you, they can be solved. If youneed help, there are other amateurs out there that are ready, willing and able to help.Just ask. PS: sometimes they also could use a hand, its called sharing the load.