RFI, EMI, EMC--whatever you care to call it--is a matter of concern to hams. The ARRL Lab devotes considerable resources to the subject of interference. It also provides technical expertise in the battle to preserve Amateur Radio spectrum against claims by other users of the spectrum wanting to use amateur frequencies for new, incompatible services.

Hams operate in a regulatory environment designed to accommodate all domestic users of the radio spectrum. The FCC is responsible for ensuring users a reasonable degree of compatibility within any band of frequencies.

Many hams have met Lab Supervisor Ed Hare, W1RFI, at ARRL-sponsored conventions and hamfests.

The ARRL Electromagnetic Compatibility Committee monitors developments in EMC and assesses their impact on the Amateur Radio Service. ARRL is in the process of performing noise studies and producing documented evidence of the interference being received by FCC-licensed services from unlicensed Part 15 devices. An excellent description of the ARRL noise study--Amateur Radio Interference Assessment--can be found on ARRLWeb.

In addition to this project, the Lab:

• Answers individual inquiries from hams (and sometimes their neighbors) about EMI problems

• Writes and publishes articles and books about RFI (see The ARRL RFI Book)

• Works with ARRL's Washington office on various spectrum and RFI-related filings before government agencies and

• Participates in standards and industry groups, including: IEEE C.63, IEEE International Committee on Electromagnetic Safety, and the Society of Automotive Engineers EMC and EMR committees. (For a survey of what automakers say about EMC compatibility see RFI-Automotive on ARRLWeb.)

Hare represents ARRL on these committees. In addition he maintains a liaison with the FCC, VDSL Committees, Home Phoneline Networking Alliance and HomePlug Powerline Alliance.

This last group, HomePlug, may not be well known to hams, but we should be aware of their existence and the consequences of their work. The HomePlug Powerline Alliance is a not-for-profit corporation formed to create specifications for high-speed home power line networking products. HomePlug devices superimpose HF signals onto the electric wiring. Therefore, a potential for interference exists. As a result of the League's involvement, HomePlug specifications include protection against interference to the ham bands.

Power Line Interference

Senior Lab Engineer Zack Lau, W1VT, assembles noise sources for use in the ARRL Amateur Radio Interference Assessment.

The majority of the complaints--about 90%--are related to power-line noise. Although power line companies have a definite responsibility to correct the interference, their staffs are frequently not well trained in the techniques of locating the offending noise sources. The Lab can help--if the company is interested in resolving the problem. We can also direct them to sources of consulting help and training for their staff.

It's interesting to note that power line interference has been the bane of Amateur Radio for a very long time. In April 1926, Radio Home Magazine published a story titled Interference that discussed power line interference problems in Lancaster, Pennsylvania. Seventy-six years later ARRL staff is still heavily involved with issues relating to power-line interference.

The next most frequent complaints have to do with consumer electronics equipment such as telephones, TV sets, computers and audio components. These devices, which were the victims of EMI for many years, are now becoming a major source of interference to Amateur Radio.

Cable TV companies are usually prompt in responding to interference complaints because they must meet stringent leakage requirements or face severe penalties. Signal leakage at frequencies used by aircraft for navigation and communication can create a hazard to the air traffic control system.

A general view of the Lab. That's Zack, W1VT, surrounded by some of his projects. Beyond the glass partition is a machine shop and a separate photo lab. Circuit boards can be created and taken to a bench or to the screen room for testing in less than an hour.

Help for the Individual Ham

Here's another of Zack's practical projects under construction in the machine shop. This antenna is designed for quick attachment to a station wagon roof rack.

In addition to working for the protection of Amateur Radio frequencies throughout the entire radio-frequency spectrum, ARRL also provides assistance to individual hams who have problems with interference from unknown RF sources. Power-line noise, cable TV leakage and telephone interference are examples. Other problems, of a local regulatory nature, may arise when hams apply for permits to erect antenna support structures.

ARRL suggests that amateurs desiring assistance first contact their Section Manager and ask for a referral to the Technical Coordinator. Most problems can be solved locally and the TC is aware of the resources available in his area. A radio club may have an RFI committee with experience in dealing with local regulators and in some cases the public utilities. It's possible that hams within the power-line company may be able to help the RFI committee solve an interference problem before the situation escalates.