Radio Frequency Interference
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Radio Frequency Interference

You may be the cause of radio frequency interference.

By Randall L. Caba

A neighbor once complained to the Federal Communications Commission (FCC) that our neon interfered with his HAM radio operation. While we had many window signs and neon art pieces there were also several neon installations lining businesses up and down the street. Still, the complaint was aimed at us and the FCC sought resolution. Several questions begged answering. What exactly is radio frequency interference? What are its causes? How do you determine if neon and/or which neon is producing the interference? And what can you do to resolve it?

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  • What is radio frequency interference?
    Radio frequency (RF) is an electromagnetic wave that oscillates between the audio and infrared in the electromagnetic spectrum. Many natural RF signals exist in nature and indeed travel throughout the universe. But typical radio frequency interference (RFI) is defined as any “unwanted” signal received by a device that prevents clear or best “wanted” signal reception. This means that RFI can affect any signal receiving system such as televisions, computers, audio and security systems, and even automatic garage door openers.

    What are its causes?
    The FCC handles a wide range of signal interference complaints, RFI is but one of them. And RFI is hard to track down. This is because any device that generates or uses radio frequency as part of its operation can also cause radio frequency interference. The interference is broadcast through the air as radio waves or conducted through power lines. Naturally, communication equipment can cause interference, as can microwave ovens, computers, street lamps, aquariums, lighting systems and other electrical devices and equipment. So, the interference may not necessarily originate with your neon signs. In fact, it may not even be your business causing the problem.

    One of our clients once thought a sign we made for him was interfering with his photographic and film development equipment but the interference changed in pitch. As it turned out, a construction company working down the street was using an industrial saw that generated noise that traveled through power lines into the photo shop. The only solution was to isolate which construction equipment caused the interference then schedule certain off-hours for its use.

    Most modern home electronic equipment and devices contain design features and circuitry to filter harmful radio signals and any subsequent electrical interaction. But often-inexpensive equipment houses inadequate filtering circuitry. This causes most complaints and the subsequent solution to land squarely back in the complainer’s lap since the FCC states that home electronic equipment “must accept any interference received.” And local authorities have no power to assist; they are preempted by federal law to act even if the transmitter is operating illegally, unlike complaints of loud music or use of noisy machinery. Hence, all RFI charges must be filed with the FCC. But here’s an inside tip, sometimes you can get home electronic equipment manufacturer’s to provide RFI filters at no charge. It’s worth a shot if you are the recipient of unwanted signal noise. But in the case of our complaining HAM radio operator, his allegation took precedence in the eyes of the FCC.

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    So, how do you determine if neon is the culprit and which neon piece is producing the interference? First, let’s make certain that someone else is not emitting harmful RFI. Turn on a portable AM radio in between stations-make sure it’s running on batteries to eliminate the chance of power line noise. Adjust it to where the interference is loudest. Now, go outside down the block and walk toward your or your client’s business. Does the interference get louder? Continue walking past the location to see if the interference diminishes. Make note if the interference increases at other locations like at a local TV or a computer repair shop.

    Then, return to your or your client’s location and turn off the main breaker. Does the interference decrease or disappear altogether or was there no change at all? If the interference decreases then you are potentially a contributor. If it ceases completely then you are the source of the problem. But if there was no change, the source of the noise is likely some other business and you need to find and report it.

    If the radio shows that the RFI increases in your or your client’s business, determine if the interference is constant; it could be the lighting system or other electrical equipment causing the problem. Roam around and through each room. Sometimes varying sound will lead you directly to the culprit. Next, turn off circuit breakers one at a time to see if the noise is generated on a particular circuit. If necessary, unplug each electrical device one at a time to determine the source.

    In a neon shop, it could be that only during bombarding a tube is the interference problematic, especially if you frequently setoff sparking the Jacob’s ladder. Or maybe it’s that aging, burn-in transformer or even that microwave oven or refrigerator in the corner. But if the noise is the loudest at an existing neon sign then it could be a malfunctioning solid-state transformer as they use high frequency electricity to aid lighting the tube. Normally, they don’t produce harmful, stray RFI but I have replaced a couple aging ones that did.

    There’s another kind of unwanted noise called sixty-cycle interference. It’s more common than broadcast interference and is one type of signal noise that neon is notorious for producing. Usually, it’s overheard on telephones and gets louder the closer the phone gets to the problem neon. The handset or handset cord picks up the interference because it acts like an antenna. The best way to rid this trouble is to house all conventional transformers and as much wiring as possible in well-grounded metal housings. Adding extra insulation to high-tension wiring prior to encasing in grounded metal will go a long way in preventing arcing. Arcing too produces RFI as well as the better-known neon failure or the least liked neon caused fire.

    A poorly wired unit can generate interference too. If you see sparks or smell ozone at the electrode wires near a tube junction, the wires are disjoined. This is usually a simple repair so long as the wires or electrodes haven’t been damaged. Also, know that excessively dimmed neon can cause trouble too. And that special AC-line filter can stop some noise from traveling over power lines. I’ve used one made for microwave ovens that sometimes halt interfering feedback through the power cord. Simply plug the filter into the wall outlet then plug the neon transformer into the filter.

    My computer uses a wireless system. When neighborhood kids play with their radio frequency controlled cars, my keyboard and mouse sometimes misbehave. Usually, the problem lasts only several seconds before the devices regain normal function. And occasionally, a country western station or a HAM radio operator wanders in on my upstairs phone line. But we have to understand that in today’s “wired” and “wireless” world, we’re as likely to be the victim of radio frequency interference as well as the assailant. If you find yourself the target of a FCC inquiry, ask them if there are other tests you can run to discover the problem source. I’ve found the FCC quite helpful. Also, try to resolve the issue first with whomever the interference issue is with. Most folks are happy to work with you.

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