Monmouth County Local Interference Committee

INTERFERENCE - What is it?

Interference occurs occasionally on all repeater systems, but what constitutes interference.

Interference Definitions

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

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

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

From the Amateur's standpoint, this means you cannot communicate. However, remember that the Amateur Service is not a safety or essential service. Some moderation must be considered (e.g. hearing a distant co-channel repeater when your local repeater is not active), while being annoying, is not "interference". Hearing adjacent channel splatter while carrying on a conversation on simplex or your local repeater, while affecting the quality of the conversation, is not truly interference. If it makes communication completely impossible, then it should be considered interference, although it still may not be harmful or necessarily willful. Take note at this point that many of the noise sources to be defined below do not affect FM/PM type radio operation except to cause desensing of the radio, possibly masking the desired signal. The interference may be from strong co-channel signals under normal or enhanced band conditions, out of band commercial sources such as Cable TV (CATV) leaks, bandits operating within our Amateurs bands illegally, an accidentally stuck PTT switch or a mobile station sitting on their microphone and other such scenarios or it may be deliberate and malicious

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

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Types of Interference:

Natural:

There isn't much that can be done about these sources.

Manmade:

Non-Radio:

Radio sources:

As you can readily see, there are a multitude of problems waiting for solutions. Each, with few exceptions, is solvable. It takes patience, perseverance and the cooperation of others.

The natural phenomena as defined above are not within our capability to solve. It is the manmade signals that by and large can be attenuated or controlled.

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Manmade "Non-Radio" Remedies:

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.

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.

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.

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 to 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 proven effective.. Monitors, because of the harmonic-rich signals that float around inside, require special attention, including RFI sprays, conductive fingers, and filtered/shielded cables.


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Manmade "Radio (Amateur & Commercial)" Remedies:

There are two basic types:

Unintentional or accidental (e.g. keying up on the repeater before turning up the volume control, or sitting on the microphone). This has happened to many of us, and those of you that haven't done it yet will sooner or later.

The other type is the harmful, willful or mischievous interference. This is intentionally tying up a repeater or frequency to prevent its use by other persons. Typical examples are the touch tone bandit, the purveyor of objectionable language, and the false cry for help. Many of these incidents are frequently reported in QST and elsewhere. The false cries for help not only cost the taxpayer in terms of manpower sent needlessly but they cost credibility to every one with a legitimate need for help. It's the classic case of the "boy who cried wolf" enough times, and no response will come.

The FCC is usually not interested in solving unintentional or accidental interference. However, habitual unintential interference, such as when the same Amateur time after time is found to be sitting on the mic while mobile due to carelessness etc. must be addressed.

The FCC is interested in rectifying harmful interference, referred to as "malicious." interference. It is rare that the FCC will get involved in an Amateur Radio interference complaint unless the offended Amateur Radio community has already done a lot of the work themselves.

When an Amateur Repeater Station experiences deliberate, malicious interference, this is called jamming. Intentional jamming can be motivated by any number of reasons and can be an annoyance unlike anything else within the Amateur Radio Service. However, take heart, it make take time, but jammer's CAN be found and with an active LIC in place, they will be found sooner rather than later and a case of evidence will be constructed that will enable the Federal Communications Commission (FCC) to take rapid action.

When you hear any interference that you suspect of being deliberate take detailed notes then complete and submit the MCLIC Malicious Interference Form.

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Conclusion:

Natural amospheric interference must be lived with

Repeater to Repeater interference is usually settled locally or regionally, by the parties to the dispute and the affected user community. Such matters, however, may come to the attention of the Amateur Auxiliary program when harmful interference is caused by a non-coordinated repeater to a coordinated repeater. The non-coordinated repeater bears the primary responsibility of cleaning up the interference, under the FCC Rules

Some co-channel repeaters have overlapping coverage areas, in which a user will hear both repeaters. This situation becomes more troublesome during band openings. The user can eliminate most of the nuisance noise by using CTCSS tone decode. This, of course, is only possible if the repeater which is desired to be hear has tone encoding on its transmitter. Many repeaters now decode tone, although they may not be encoding tone. Some repeater sponsors, because they know that many of their users will experience problems of overlapping coverage, are encoding even though they do not normally require PL access for their use.

On the other hand, if the repeater itself experiences increasing incidences of distant users of other machines keying it up, tone decoding may be necessary. Many repeater owners have hesitated to install tone-decoding options on their repeaters. However, it may be necessary to insure that some of the man-made and natural interference does not constantly key up the repeater.

Cures or at least remedies are available for most man made interference from various devices. Time and effort is required to determine the source of the interference and often thereafter to get the owner of the source to take responsible action.

Accidental man made interference is a fact of life, however, if indiviuals are known offenders, they will need to be addressed.

Deliberate, malicious inteference will not be tolerated and all Amateurs need to monitor, record and submit details as to what they have monitored to assist in the identification and apprehension of the person(s) involved.

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Latest update: 17 October 2002