July 27, 2007 4:00 AM PDT

FAQ: The 411 on radio frequency interference

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.

See more CNET content tagged:
radio frequency, consumer electronics, cell phone company, interference, radio


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It's not a problem for all carriers
Well, "carriers" mis-characterizes the issue, its the network technology not the carrier. Having a CDMA phone since before verizon was verizon, I had never experienced this. I have upgraded to phones with increased capabilities through the years and no "buzz" from ANY phone. Then, I was issued a Blackberry from work that had Cingular service. Different freqs, different coding scheme, etc etc. Now I have the problem, computer speakers, car stereo, everything.

Want to get rid of it? Get a CDMA carrier.
Posted by GOV_Stooge (2 comments )
Reply Link Flag
Does appear to be GSM phones only
I'm a great fan of GSM phones, but I also have noticed that they seem to be the only ones that give this sort of interference, although it varies from phone to phone. I constantly have a CDMA LG VX8300 next to my monitor at work, and don't have any interference, not even when it rings.
Posted by exjoburger (13 comments )
Link Flag
100% Correct!!!
I have also had Verizon Wireless Service which uses CDMA Technology. I've had it for about 10 years and NEVER had that problem, that's why i prefer CDMA over any other Technology, because that buzz is really annoying, prior to verizon i use to have AT&T and then NEXTEL and had that problem with both carriers. i think is something with GSM and EDGE Technology.
Posted by conazo (2 comments )
Link Flag
This is correct, but here's why:
All cell phone systems need a way to allow multiple users on the same tower. GSM uses TDMA (Time Division Multiple Access), so each user transmits a short burst of information at a different time, so they don't interfere with one another. A GSM phone sends one packet (burst) of data every 4.615ms, or about 217 per second. Your speakers are being interfered with at 217Hz, causing the buzzing sound.

This does not occur with CDMA (Code Division Multiple Access). In CDMA, each user gets a different code applied to his signal, so the base station can separate the users apart that way. This allows all users to transmit at the same time, so the radio isn't switching on and off at 217Hz (or any other rate in the audio spectrum).

I used to have Cingular, and I amazed everybody when I would pick up my phone to answer the call before it started ringing :-). Can't do that anymore with Verizon, but I'm glad the interference is gone.
Posted by silenthorn (5 comments )
Link Flag
I have Verizon CDMA and still have the interference problem. There is a partial solution though. Put your phone in airplane mode. You won't be able to get phone calls but 4g still works.
Posted by patentcolo1 (2 comments )
Link Flag
Amiga 1200 frozen with GSM interference
I remember having Motorola 68020 CPU Amiga 1200 and when
cell phone rung, it got frozen. Freezing (e.g. BSOD) wasn't even
known on Amiga unless you get somehow infected by one of
rare viruses.

Of course Amiga 1200 was a computer from 1993. The
electronics engineer forgot to tell ONLY the electronic devices
having special workarounds in GSM age isn't effected from cell
phones. They are designed in a way not to fail or get real actual
effect from that huge interference.

For example, if you got a car with ABS made before cell
phones, e.g. a very good quality Mercedes you can't give up
from 1991, you better ask your car manufacturer whether to
use ordinary cell phone while driving or buy a car kit (real one
with ex. antenna).
Posted by Ilgaz (573 comments )
Reply Link Flag
Not a problem for all phones
I had my Nokia E61 sitting on a conference table next to my colleague's new iPhone. The Polycom on the table (which seem to be even more susceptible to this interference than many other devices) kept buzzing periodically as both our devices checked email. When the buzzing got louder, I moved my phone away... but it didn't stop until my colleague moved his iPhone. I then did an experiment and made a call with my phone and there was only slight interference. I guess the "i" in iPhone stands for "interference".
Posted by SnidleyWhiplash (61 comments )
Reply Link Flag
It's about the noise...
At the end of the day, it doesn't matter to as an Producer and audio engineer whether a particular phone "works" with something or not... All phones are banned in the studio, period. I'm surprised anyone cares if the iPhone produces interference or not. People need to learn to turn their cell phones off when appropriate anyway.
Posted by mattumanu (599 comments )
Reply Link Flag
FCC seldom acts on this type of RFI
The FCC considers that it doesn't need to regulate manufactured electronics, and allows sloppy designs to be imported to the US. It could act, but wants to "deregulate" wherever possible. Imagine what would happen if FDA did that (oops, it does!).
Posted by tpobrienjr (15 comments )
Reply Link Flag
Finally, someone explains this!
This is extremely irritating and it must be stopped from becoming more prevalent! I have been increasingly hearing the "dit-dit-dit-dah-dit-dit-dit-dah", through my desktop PC speakers, even when the PC is turned off, on my car radio on an AM station, and in a customer's conference room on their speaker phone. So - the culprit is GSM cell phones, which fairly recently came onto the U.S. scene? So, CDMA is better after all! We are in San Diego, so I was thinking it was military radio interference... It is very irritating, especially when you are recording any audio into your PC for your MP3 player...
Posted by MTiddens (2 comments )
Reply Link Flag
Sounds like Blackberry's & I-Phones have the problem!
Based on the comments so far and me also having a Blackberry with Cingular service, it sounds like the Blackberry's and I-Phones have this problem. They should have not passed FCC testing! The FCC must step on these companies (the designers) before "smart phones" proliferate further! Can't blame this one on "China"...
Posted by MTiddens (2 comments )
Reply Link Flag
I just happen to own a set of cheap made in China speakers.
They start to 'oscillate' a few seconds before the Motorola
actually rings. So I can pick up the phone before it rings---
freaks out people around me. ESP.

On the other hand, I can't believe they devoted an article to RF
interference. There will always be cross-talk. I would have
thought readers who frequent CNET have at least a very basic
scientific or technical background and understand exactly what
the sticker from the FCC, which adorns all of our electronics,
actually means.
Posted by Rick Cavaretti (216 comments )
Reply Link Flag
Missing the point...
Lots of folks seem to be missing the point - cell phones and
other similar devices (two way radios) are designed to emit RF;
that's how they work. And since we are all looking for better
performance out of these devices, the manufacturers will
continue to ramp up their output power and cause even more
interference. The real fault here is crappy shielding and
grounding schemes that are so prevalent in 'consumer' & 'pro-
sumer' level audio devices. The RFI is only heard if the
interference has a path into the amplification circuit - block the
path and the interference disappears.

There are audio mixing consoles out there that a five watt radio
can be right beside without a problem, and other (less well
designed) ones that the radio can't be within ten feet without
causing RFI problems.

Not the radios fault -- its the audio manufacturer's.
Posted by SonicL (3 comments )
Reply Link Flag
its not just gsm
its cdma as well, and any rf device
Posted by zrogerz69 (20 comments )
Reply Link Flag
just kidding
guess i'm an idiot haha
Posted by zrogerz69 (20 comments )
Link Flag
it's common for phones
My phone, a nokia 6101, makes these weird radio frequency through my speakers whenever someone calls or texts me. Most phones should do that because of a signal that is going through your speakers into your phone. It should be anything to be worried about. At least I know when about to get a call or text now!
Posted by snypervictim (3 comments )
Reply Link Flag
it's always been here but no one made an issue out of it
The issue has always been here but no one has really made an issue out of it. The problem is the comsumer electronic devices that are cheap and not properly shielded. The cheaper they get the more interference they get. Also, in general, the better the phone gets a singal the more likely it will cause such interference.
The problem should have been more obvious years ago with the first generation GSM phones should it had been GSM's fault because back then there were not strict regulations with regard to the RF emission of those phones, and I believe they did emit much more RF than modern models do. I suppose back then we had more quality comsumer products. The cheaper the computer parts were getting over the years the more I was noticing this interference problem. In fact, the first time I personally noticed this issue was when I changed an old but quality Sony monitor for a newer but cheaper Samsung model.
I believe we'll see more and more of this issue in the years to come because the world only is going to see more and more of RF emiting devices, such as phones.
Posted by skareta (13 comments )
Reply Link Flag
happens on my desktop speakers i pick up emergency band
every once in a while my local fire dept down the street or the police parking depot behind my house, will cause my speakers on my desktop computer (altec ) speakers to pick up their band and i would clearly hear the communication from a car or truck.

It tends to be really loud and it actually cranks up the volume on its own. Happened on a few night where I would get freaked out when all of a sudden I would hear this screaming sound right next to my head almost. Learned my lesson to turn the speaker off at night...then it won't pick up anything.
Posted by dondarko (261 comments )
Reply Link Flag
Shield the plane's equipment !
I can't believe my safety online is put at risk of someone tripping their WIFI, bluetooth, or cells on (even while bouncing in shaking luggage at the worst possible moment when flying through air pockets); so either a) it is not really an issue and so the spurious warnings need to stop, or b) it is and issue and sensitive instruments should be shielded rather than have their continued operation be dependent on luck.
Posted by Rants&Raves (199 comments )
Reply Link Flag
Happend all the time
My friends and I used to have SPRINT/NEXTEL phones and that interference happened all the time when we were watching tv, listening to music at home or in a car, pretty much whenever we were near any device that had an audio output.
Posted by plogue87 (14 comments )
Reply Link Flag
Now you know why airlines are worried
Just imagine the number of phones and mfgrs types that could be onboard your next flight. Then imagine what kind of interference would be created and the multiple harmonics that would be generated when half of them are in operation. I would be almost impossible to sheild any equipment from all that RFI generated by those onboard devices. I think the airplane is the one place these devices should be forbidden from operation.
Posted by mjd420nova (91 comments )
Reply Link Flag
Killeen Texas Computer Nerds - Copper Foil
A very inexpensive way to eliminate this problem is to use copper foil and create an RFI shield around the emitting components. This can be done without causing thermal damage to surrounding components. The Government uses similar principals in RFI shielding of Mil. Spec. equipment.

Check Out These Sites:
<a class="jive-link-external" href="http://www.tech-faq.com/tempest.shtml" target="_newWindow">http://www.tech-faq.com/tempest.shtml</a>
<a class="jive-link-external" href="http://www.computernerds.net/nerd/index.asp" target="_newWindow">http://www.computernerds.net/nerd/index.asp</a>
Posted by thetopnerd (17 comments )
Reply Link Flag
OMG My subwoofer...
I think my home theater subwoofer has been making random noises because of this! Now that I think about it, it started about the time I got the iPhone, and I have been keeping it in my pocket when we watch movies...
Posted by count0--2008 (38 comments )
Reply Link Flag
Thanks soo much for the informative story!
Thanks soo much for the informative story!
Posted by shmody (71 comments )
Reply Link Flag
This is news?
GSM Blackberries have always had this problem, many quite badly. Most BB users know instinctively to keep it away from speakers to avoid the annoying tehcno if EMI. Plus the running jokes about not stowing it in your front pants pocket if you want to retain the ability to reproduce.

Glad to see that industry appears to be moving towards eliminating this annoying issue.
Posted by madmatt (6 comments )
Reply Link Flag
No, its not just GSM....
Ive been a Nextel subscriber for almost 10 years now, and been through about a dozen phones. Throughout that time, ive always had to deal with this kind of thing. In case you dont know, Nextel is using a technology developed by Motorola in the early 90s called iDEN, which runs at a fairly low frequency as far as cell phones go. The kind of RF interference experienced by many cell phone owners is a disruption in the RF band, and it doesn't only happen with frequencies that are close together either, it can happen all over the RF band. If a device isn't properly shielded, it can disrupt all sorts of devices, but speakers are especially susceptible because of the exposed magnet and their overall design.

Just wanted to dispell anyone believing it was ONLY GSM phones. iDEN is older than any current US technology by the major carriers ( It just took awhile for a carrier in the states to pick up teh technology, ie Nextel.
Posted by usb123 (1 comment )
Reply Link Flag
One time in church, I was giving a talk and i got a very large
amount of interference as a text message was being delivered. I
had to step away three feet before it would stop, lol.
Posted by mineralwalker (5 comments )
Reply Link Flag
There is a partial solution. Put your phone in airplane mode. You won't be able to receive calls but emails will still come in since 4g still works.
Posted by patentcolo1 (2 comments )
Reply Link Flag

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