Cellphone interference (with aircraft electronics)

News Type: Other — Fri Jun 9, 2006 7:22 PM EDT

technology, electronics, cellphone, interference

Whenever I am boarding a plane, the flight attendance usually warn us to turn our cellphones off. It is said that the cellphone can create an inteference with aircraft (navigation and communication) system. Is it true?

Well, I don't know whether it is true or not, but you can do the following experiment. Put your cellphone right next to your TV set. Turn your TV set on. Then, call your cellphone. You can see or hear inteference on your TV. Usually the audio is more noticeable. So, there is interference. The thing is, eventhough the frequency used by cellphone is not the same as the frequency used by TV (VHF / FM) there is inteference.

You can do a similar experiment by placing your cellphone right beside your computer monitor (not LCD though). Turn your monitor and computer on and call your cellphone. Your monitor screen will "dance" indicating interference!

Designing electronic circuits that are free from interference is not easy. Being an electronic designer I know that. In IEEE Spectrum magazine (May 2006) there is a letter to the editor that says that electronic calculator could also create interference. This man was on a plane and was using his cheap credit card-sized calculator. Everytime he hit a button on the calculator, indicator on the plane swings. Yikes!

In anycase, I turn my cellphone off whenever I am boarding an airplane. Would you do the same thing?

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{"commentId":155312,"authorDomain":"kikaiju"}

kikaiju

Not all phones and phone signals are equal.

My old GSM1900 phone used to cause a fit in any audio device it happened to be around, but only when the phone was actually talking to a cell tower. My newer CDMA phone does not cause any noticable interference in anything.

The interior of an aircraft is a special environment but aircraft are not inherently vulnerable to cell traffic otherwise they'd be falling out of the sky every time they passed over a cell site, which operate a much higher power than any handset.

I can think of one particular cell site on a hill overlooking the approach path for a major airport. There are 8 different carriers using that site less than half a mile from the landing planes. No issues.

Just last weekend, I used my cellphone from the cockpit of a plane while in flight. No issues.

There are also plenty of broadcast TV and radio towers operating at power levels hundreds of thousands of times stronger than the strongest cell tower, but aircraft seem to survive.

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#1 - Sat Jun 10, 2006 6:30 AM EDT

{"commentId":175240,"authorDomain":"budi"}

Budi Rahardjo

kikaiju, even no aircraft has gone down because of cellphone that does not mean that there are no interference. There's probably still interference but the effect is very small. It all depends on the (electronic) design.

When you talk about cell site on a hill that it does not interfere with aircraft, it is understandable. The cell site (tower) only emits signal with certain frequency (say, 900 MHz or 1800 MHz, or whathever). There is probably other frequencies, but they are small. But, when we talk about cellphone or electronic equipments, sometimes they emit signal that's not in their spec. This signal may not come from the RF part of the equipment (ie not emitted from the antenna), but from the electronics in other parts of the device. Maybe the signal come from that part that's handling user input (touch pad, lack of debouncing signal), output (audio), or even power supply. The thing is, it's hard to design a fullproof electronics circuits. It can and should be done, though.

My point is that it is possible to create interference. Fortunately, the effect is usually negligible.

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#2 - Fri Jun 23, 2006 6:18 AM EDT

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BUDI RAHARDJO

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Cellphone interference (with aircraft electronics)

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