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Table of Contents

1. Where does Radio Frequency Interference (RFI) originate?
2. What effect does Radio Frequency Interference (RFI) have on systems and data?
3. How can Radio Frequency Interference (RFI) be controlled?

Where does Radio Frequency Interference (RFI) originate ?

The short answer is: from the same place that spikes/surges come from - Lightning, man-made electrical equipment noise and various transmitting equipment., Actually, Radio Frequency Interference is always associated with spikes and surges.

Lightning, the Mother of all Spikes, radiates radio energy across all bands from VLF to microwaves. Other weather conditions, known as spherics, also generate significant energy which often results in small electrical discharges, generating Radio Frequency Interference. While not as severe or dramatic as lightning, serious communication interference can result.

But there are other types of interference as well.

Radio stations, cellular phones, Citizen's Band and police radio, welding equipment, small office or household appliances, fluorescent lights, loose electrical connections, defective AC Power plugs, cords or sockets are among the many sources of electrical interference.

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What effect does Radio Frequency Interference (RFI) 
have on Systems and Data?

Interference is aptly named. The name came from the earliest days of radio when so-called static from various sources "interfered" with radio reception. This concept carried forward to television and ultimately to computers and other communication equipment.

Interference may cause erratic program operation; or it might cause errors in data processing (we've all heard the old anecdote of a $1,000,000 check being issued for a $1 refund).

In imaging - erratic, undesired color shifts might occur.

Communication may be disrupted or completely unintelligible.

Surveillance or Computer monitors may wiggle and sway - sometimes in step to the local rock and roll radio station down the street!!

Surveillance cameras and associated video monitors may show shadowy background patterns.

Audio systems may "play" local radio or TV programs. Other times the audio system may reproduce noise from fluorescent lights or diathermy equipment.

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How can Radio Frequency Interference (RFI) be controlled?

Two approaches are usually taken for interference control.

1. Apply suitable preventative measures to the interference source. Of course, to accompolish this, the interference source must be identified. Even if identified, it is often impractical or impossible to taken corrective action. For instance - you can't do anything at the radio station.

For those noise sources that can be identified and accessed, a good first step is to ensure regular, thorough electrical maintenance of equipment suspected of being the interference source. Be certan all electrical connections are securely tightened.

When positive you have identified the interference source, install suitable filtering and suppression to bring interference under control. Very often a single socket (Industrial Grade) stand-alone power line filter-suppressor or a wire-in filter-suppressor solves the problem. Industrial equipment may require Twist-Type , Extreme Duty, or other Hi-Current filter-suppressors. Install filter-suppressors as close as possible to offending equipment.

While at the interference perpetrator, verify that all required grounding is in place and grounding screws are securely tightened. Since Radio Frequency Interference may emanate from many portions of the offending device, shielding efforts may be required in severe situations. Use great care to be sure any shielding installed is sturdy and safe. Also, be certain any installed shielding does not impede normal cooling air flow

2. Apply Radio Frequency Interference control steps at equipment suffering interference (victim). This is usually the route taken because it is often impossible to isolate or work on the suspected interference source.

Depending on the amount and severity of interference the equipment encounters, you could install an AC power line filter-suppressor, a KLEEN LINE^® Regulator-Isolator-Conditioner or a KLEEN LINE^® Isolation Transformer directly at the system. This is particularly effective if RFI is entering equipment over the power lines. Often, folding up the power line between equipment and filtering device will bring an added measure of relief.

Industrial equipment may require Twist-Type or Hi-Current filter suppressors.

Should further relief be required, investigation should turn to cables entering the affected equipment. Speaker or pre-amp cables in audio systems; incoming signal cables in remote terminal monitors; data line or network connecting cables; phone lines; street cable in cable tv units

3. Modem interference originating over Phone lines is discussed in our Modem & Phone section. Models generally used to provide interference relief for phone line connected modems or other equipment are PDS-11 and TURBO. These units have integral RFI filtering networks, very effectively isolating affected equipment from the attacking RFI energy. In addition to effective RFI filtering, these units very High Performance Spike Suppression systems, providing total equipment protection.

Severe Modem and Phone interference has successfully been countered by installation of our TURBO-MAX on incoming phone lines.

Direct wire or Din rail versions of these models are available

4.RFI interference control is discussed in our Network & DataLine page, on our Security / Surveillance page and on the Video page.  A wide array of products are presented for RS-232, RS-485, RS-422, 10Base-T, 100Base-T, Ethernet, video, camera and phone lines. Although most units shown in the network and data line sections are protectors only, Electronic Specialists has been successful in applying RFI reduction techniques to all areas of communication, computing and surveillance equipment. Contact our Engineers for help with your RFI problems

5. Video terminal, cable TV, Satellite receivers and computer monitor interference is discussed on the Video page. Solutions for many problems are offered.

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