Electronic Products Word of the Week: Electromagnetic interference

Electromagnetic interference (EMI) is electronic noise, which is never wanted in an electronic system and can be downright dangerous when it interferes with critical electronics, such as medical equipment or airplane guidance and communications systems. EMI is in the news again with the report from Travelers Today that the Federal Aviation Administration (FAA) is considering relaxing the ban on the use of electronic devices during takeoff and landing. Its recommendation is expected to be released in September. 

EMI takes several forms, with related acronyms RFI and TVI, radio frequency interference and television interference. As the son of both an amateur radio operator (known as a ham) and a television repairman, I knew firsthand in the 1950s and early 1960s about both. When they were present, RFI and TVI made it impossible to enjoy radio and television. Here's why: Television begins with Channel 2 and is preceded by Channel 1, which was removed from the broadcast spectrum (see below) early on as a community television reservation and given to amateur radio and other uses. But that didn't mean that signals always stayed where they were supposed to.

Source: http://en.wikipedia.org/wiki/North_American_broadcast_television_frequencies

As Mel Berman of TDK-Lambda Americas pointed out in Electronic Products Magazine in October 2008, “EMI can be in form of conducted EMI, which means the noise travels along electrical conductors, wires, printed-circuit traces, or electronic components such as transformers, inductors, capacitors, semiconductors, and resistors. Electrical noise can also be in the form of radiated EMI (RFI), noise that travels through the air or free space as magnetic fields or radio waves. RFI is usually controlled by providing metal shielding that contains the magnetic fields or radio waves within the equipment's enclosure.”

Thanks to the abundance of attention EMI has gotten over the years, electronic devices emit less noise and plane equipment is better insulated. (If you want to immerse yourself in the progress the electronics industry is making in curbing EMI, click here for Electronic Products Magazine 's extensive coverage of the topic over the years.) Analog cell phones were more of a problem than digital, and today all cell phones are digital since 2008, when the last analog cell phone network was deactivated and dismantled. Digital networks eliminate crosstalk by design – and crosstalk is yet another form of EMI. (A previous article in this series noted that the Privacy Rights Clearinghouse points out that most wiretapping devices emit no audible sounds. If you hear others talking on your phone, you may simply be experiencing “crosstalk,” a common phone problem that is simply unwanted signals in a communication channel, whether intelligible or unintelligible. For example, cordless telephones may pick up others' conversations when two cordless phones are tuned to the same channel.)

The Federal Communications Commission (FCC), whose headache it is to regulate electronic noise, had asked the FAA to ban cell phones, but when engineers solved the analog problem, the FCC is no longer the reason you can't use your cell phone during flight. As Mark Nelson in Media & Tech points out, “Although there has never been any evidence found of aircraft malfunction from electromagnetic interference (EMI) from a consumer electronic device compliant with Part 15 of the FCC code governing EMI emissions, there is no proof that it's NOT dangerous either. Theory says it could happen, but many hypothetical events could happen that don't. The FAA was just erring on the side of caution, and people were already abiding by the ban on in-flight analog cell phone use anyway.”

The American Radio Relay League(ARRL), a not-for-profit membership-services organization representing the interests of hams, has long-standing relationships with groups and organizations such as the FCC, the National Cable Television Association, and the Electronic Industries Association. All of these organizations have active interference-reduction programs. In one publication, the ARRL advises: “The term 'interference' should be defined without emotion. To some people, it implies action and intent. The statement, 'You are interfering with my television' sounds like an outright accusation. It is better to define interference as any unwanted interaction between electronic systems — period! No fault. No blame. It's just a condition.”

Nevertheless, EMI is a condition that everyone knows must be stopped. For instance, the ARRL notes that “among the more difficult problems faced by the cable TV industry are those caused by leakage or ingress,” yet other terms for EMI. “The effects of these problems are felt from the front-office staff that has to deal with the paperwork associated with all of the applicable regulations, to the maintenance personnel in the field dealing with subscriber picture quality. Leakage is a two-way phenomenon; when signals can get out, over-the-air signals can also get in.”

In a publication on pacemakers, the ARRL says, “The American Heart Association has a page on Pacemakers. It contains the following quote: 'CB [citizen band] radios, electric drills, electric blankets, electric shavers, ham radios, heating pads, metal detectors, microwave ovens, TV transmitters and remote control TV changers, in general, have not been shown to damage pacemaker pulse generators, change pacing rates or totally inhibit pacemaker output.'”