Waves of Trouble

Digital and wireless systems are on a collision course.

I just turned on my electric shaver by dialing my cell phone. This was not a Stupid Bluetooth Trick. I just happened to notice my Norelcos battery lights blinking when I put the phone down on my desk at the end of a call. I found that if I made the phone ring, I could start the shavers blades spinning.

Like the bizarre events at the beginning of the movie "Ghostbusters," this interaction serves as a warning of trouble in an unseen realm. Digital systems on the frontiers of price and performance, and wireless systems in both work spaces and public places, are on a collision course defined by physics—and complicated by attempts at creative regulation.

The resulting crash can be prevented only by rigorous engineering and acceptance of associated costs, combined with responsible operation.

My shavers surprising remote control feature is not the only omen of trouble.

As this year got under way, the Federal Communications Commission fined Datel Design & Development $10,000 for importing 15,000 TalkNet USB headsets that exceeded regulatory limits on "unintentional radiators," devices whose function doesnt actually require a radio transmission.

Intentional radiators, like Wi-Fi cards and hubs, are the obvious parts of the wireless management problem. No less essential, however, is the need to monitor other digital devices for regulatory compliance because fast-switching digital signals are rich in energy at several higher multiples of their frequencies. Inexpensive wires, without the shielding that adds weight, bulk and cost, make excellent antennas.

And if electromagnetic principles arent doing enough to create anarchy, why not add politics and economics to the mix? This year began with the FCC exploring "cognitive radio," the use of software-controlled devices that follow complex rules involving time, location, power level and frequency to enable voluntary sharing of spectrum, in place of todays more restrictive licensing by classes of user and service.

Its attractive to imagine the use of increasingly affordable processing power to make radios cooperate for more efficient use of spectrum. The goal is a system not unlike what we have inside our heads. The human ear and brain perform miracles of distributed signal processing, with the ear acting not as a mere microphone but actually receiving commands from the brain that make the cochlea suppress unwanted noise. A skilled radio operator can decode a Morse code transmission, for example, despite other code signals or voice transmissions that are audible at the same time. Electronic systems also need deliberate design to be robust in the face of interference.

What Ive seen, however, in 35 years as a ham radio operator is that most people have no practical knowledge of radio interference principles or of their responsibilities under FCC regulations. When TV sets were connected to rooftop antennas instead of cable feeds, and most hams worked at wavelengths of tens of meters, the fifth harmonic of a 14MHz "20-meter" transmission would readily wipe out a signal on TV channel 4.

It was the amateurs job to ensure that this and other forms of stray energy were kept within regulatory limits by proper design and adjustment of transmitting equipment. But it was the job of TV manufacturers to make sure that a clean radio signal didnt overload the input circuits of the TV set and create the same effect as unlawful interference within that receivers circuits. Inexpensive TVs often failed to meet this obligation, but their owners typically blamed the nearest ham.

The twin responsibilities of avoiding unlawful emission while also rejecting lawful but undesired signals remain today but are at odds with customer demand for convenience and low price.

And as for my dial-a-shave, Im sure alert readers will detect the discrepancy between the photo at the top of the page and the notion that I even own a shaver, let alone keep it close at hand. Suffice it to say the photo has been overtaken by events.

Your own image of separate wired and wireless systems is similarly at risk of being overtaken by increasingly exotic forms of radio-frequency interference. Wireless system designers, buyers and users need to understand technologys limits and the requirements of law.

Technology Editor Peter Coffees e-mail address is peter_coffee@ziffdavis.com.