FAQ: The 411 on radio frequency interference

Ever wonder what causes that annoying "buzz" from a speaker? It's called radio frequency interference.

Marguerite Reardon Former senior reporter
Marguerite Reardon started as a CNET News reporter in 2004, covering cellphone services, broadband, citywide Wi-Fi, the Net neutrality debate and the consolidation of the phone companies.
Marguerite Reardon
7 min read
Your brand new Apple iPhone is sitting next to the PC on your desk at work as you're typing away, listening to some music from your computer's speakers, when all of a sudden you hear it.

It might start out as a "hiss" or a "dit-dit-dit-dah-dit-dit-dit-dah" like someone sending you a message using Morse code. And finally your iPhone rings, and your speakers blare out a full "buzzzzzz!" Your computer monitor also starts going a little berserk with static-like lines flashing on your screen.

"What is happening?" you ask, jumping up from your computer.

In a nutshell, you've just experienced radio frequency interference.

This annoying phenomenon is not unusual. Message boards all over the Web are filled with complaints from iPhone users about this very problem. But it's not just iPhone owners that struggle with RF interference, loads of cell phone users have experienced the same issue for years. And everyone from cell phone manufacturers to operators admit that there isn't much that can be done to stop it.

In this FAQ, CNET News.com spells out what causes this annoying "buzz" and how you can minimize the impact.

So what causes the buzz?
Basically, what is happening is that electromagnetic energy that is being transmitted from the phone is being detected and amplified by speakers. But it's not just speakers that can be affected. Computer monitors, car radios, public announcement systems, TVs, audio recording equipment and even traditional landline phones can also experience the same interference.

Can this wireless interference cause damage to any of the consumer electronics or PCs that it's interfering with?
Not really. The interference is generally more of an annoyance than something that can cause serious damage to another device. But some audio engineers and TV producers say that they require people in the recording studio or on set to turn off their cell phones to ensure that the static or buzz doesn't make its way into a recording or show taping.

If this is such a common problem, why don't cell phone manufacturers or the Federal Communications Commission do something about it?
Well, the short answer is, it's not really their fault. Cell phones are designed to emit radio frequencies and to have two-way communications with nearby cell phone towers. Phones are constantly pinging cell towers to update them on their location. And the towers are pinging phones to make sure they're still in a particular cellular area. The phones themselves are operating within the range that the FCC has deemed safe. And the mobile operators, whose networks these phones operate on, are all transmitting signals from their cell towers only within the spectrum bands that they have been allotted from the government.

So who is to blame and how can this noise be stopped?
The real culprits are the speaker, car stereo, PC and other consumer electronics manufacturers for not designing their products to fend off this interference. With proper metal enclosures for motherboards and for wires that connect into these electronic components, the device can be shielded from picking up and amplifying stray radio frequency.

The problem, of course, is that many of the components and the products themselves are manufactured on the cheap overseas in places such as China and South Korea. And over the past couple of decades consumers have grown accustomed to getting PCs and other consumer electronic devices for bargain basement prices.

Cell phone manufacturers are working with the consumer electronics industry to come up with a new standard that will help provide guidance to manufacturers so they can build shielding into their products. But this will no doubt raise prices.

For now, even if consumers are willing to pay more for a particular product, it's very difficult to know if the speakerphone or car stereo they've just bought will be properly shielded from RF interference.

Apple has recognized this problem. And it's posted a notice in the FAQ section of its Web site about the iPhone urging iPhone users to look for a logo on products that says "Works with iPhone." These audio accessories should be free of any interference.

The cell phone interference issue seems to be a bigger problem for people using certain carrier networks. Why?

It's true, customers on AT&T/Cingular, T-Mobile and the old Nextel networks experience this problem more frequently than those on Verizon Wireless and Sprint networks. The reason is that AT&T/Cingular, T-Mobile and Nextel use cell phone technologies that use a radio channel access method known as TDMA (time division multiple access).

Networks for AT&T/Cingular and T-Mobile are built on GSM (Global System for Mobile Communications), while Nextel uses iDEN (Integrated Digital Enhanced Network). These TDMA-based technologies allow several users to share the same frequency channel by dividing the signal into different timeslots. The users transmit in rapid succession, one after the other, each using his own timeslot. This allows multiple stations to share the same transmission medium or radio frequency channel while using only the part of its bandwidth they require.

Because these networks operate in a "time division" fashion their radio frequency transmitters are turned on and off at fast rates. And this can often be picked up by nearby devices.

"Most people have just learned to deal with it. The alternative is to live without wireless, and who would be willing to give up their cell phone?"
--Craig Mathias, analyst, Farpoint Group

Verizon and Sprint's network use a technology called CDMA (code division multiple access). It does not use TDMA for sharing channels. CDMA transmitters are transmitting signals almost constantly, so they don't cause the interference buzz.

GSM and iDEN are 2G technologies. Will this problem still occur as mobile operators migrate to 3G technology?
It shouldn't be as prevalent. AT&T/Cingular has built its 3G network using WCDMA, which is based on CDMA technology. So new 3G phones on AT&T's network should not have as many interference issues.

Is there anything consumers can do to reduce this problem?
Unfortunately, the answer is no. The best solution is to turn off cell phones when you're near a speaker or some other device that is amplifying the cell phone signal. Or you can try to stay far enough away from speakers and other electrical equipment if they're turned on. For example, if you're on a conference call using a speakerphone don't put your phone on the table next to the speaker.

Hospitals for years have banned cell phones, but can cell phones really interfere with medical equipment?
Hospitals use sensitive equipment such as ventilators and ECG (electrocardiography) monitors for patient care. And just like TVs or speakers, some of this equipment is susceptible to electromagnetic interference.

But some hospitals are starting to lift the ban on cell phones as newer digital cell phone technologies and better shielding on hospital equipment have decreased the potential for interference. Plus the ban is nearly impossible to enforce.

Still, some hospitals have kept the policy in place, mainly to keep noise levels down so that patients aren't disturbed by people gabbing on their cell phones.

Do cell phones interfere with communications on airplanes?
Experts have debated for years whether it is safe to use cell phones on airplanes. Most of the evidence suggesting that it interferes with aviation equipment is anecdotal. But last year, researchers at Carnegie Mellon University concluded that cell phones can disrupt normal operation of key cockpit instruments, especially Global Positioning System receivers, which are increasingly vital for safe landings, according to Bill Strauss, an expert in aircraft electromagnetic compatibility at the Naval Air Warfare Center in Patuxent River, Md., and one of the researchers who conducted the study. Strauss said risks are caused by radio emissions from cellular calls that are higher than previously believed.

Is that the only reason why the FCC and Federal Aviation Administration have banned cell phone use on planes?
There is another reason why the FCC isn't keen on allowing people to chat on cell phones while flying. The problem is that when cell phones are used in flight they are traveling rapidly over hundreds if not thousands of cell phone towers. As the plane flies over these towers, the cell phones inside the plane are connecting and disconnecting from various cell towers much faster than was intended. The rapid signal hand-off from tower to tower of hundreds or thousands of cell phones flying overhead could disrupt service on the ground, affecting millions of cellular customers.

What about other consumer electronic devices such as iPods and laptops? Why do those need to be turned off too?
Actually, the Carnegie Mellon study also found that other electronic devices such as laptops and handheld games can send out potentially harmful signals that interfere with aviation equipment.

The bottom line is that RF interference is a fact of life, says Craig Mathias, a principal analyst for Farpoint Group.

"Most people have just learned to deal with it," he said. "The alternative is to live without wireless, and who would be willing to give up their cell phone?"