Why Your Clock Radio Is All Abuzz About iPhones 397
blackbearnh wrote in with a story that's not really about the iPhone, but if your office speakerphones beep like mine does, read on: "If you own an iPhone, you may have noticed that it has a distinct and very annoying effect on clock radios, computer speakers, car radios, and just about anything else with a speaker. The folks at O'Reilly Media aren't immune, so they set out to discover just what is it about iPhones that makes them such bad RF citizens. The iPhones aren't the only bad apples in the cell phone basket and there's not much you can do about the problem. We're really in an interesting time in that there has never been so many high-powered personal transmitters just wandering loose in the world."
GSM Buzz (Score:5, Informative)
All GSM phones do that! (Score:5, Informative)
Maybe it's just because you guys aren't used to GSM cellphones but over here in the UK everyone recognises that noise. Anytime you put a mobile next to speakers you get that noise.
Welcome to the 1990s, America!
Do those people think Apple reinvented... (Score:5, Informative)
...everything regarding cellphones? Including, in this case, sometimes annoying side effects?
This is nothing new...especially if, on any other phone, you have also kept semi-constant GPRS connection.
PS. Rearranging speaker cables/etc. eliminates the problem anyway...
Re:Nothing to see here. (Score:5, Informative)
Re:Nothing to see here. (Score:3, Informative)
Re:Huh... (Score:5, Informative)
Yes, speakers which are magnetically shielded to prevent affecting CRTs will also likely reject the GSM buzz.
The clock radio would only pick up the GSM buzz if the speaker was on (radio or buzzer); when it's off, no problem.
There is a relatively easy fix for this (Score:3, Informative)
Re:FCC Rules Part 15 (Score:5, Informative)
whatever happend to the label on the bottom of everything, which states that:
"This device complies with Part 15 of the FCC rules. Operation is subject to the following two conditions: (1) the device may not cause harmful interference, and (2) the device must accept any interference received, including interference that may cause undesirable operation."
obviously the folks that made my PC speakers obeyed those rules, so why is apple getting away with breaking condition 1?
The iPhone isn't operating under Part 15. It's licensed. Your cell provider holds the license from the FCC. They paid a lot of money for it; remember the spectrum auctions that raised billions. It's your speakers that have to live with the licensed world, not the other way around.
The same is true for broadcast radio, TV, police, fire, ambulance, business radios, taxi dispatchers, amateur radio, military, and even foreign licensed broadcast systems. Your speakers have to live with it.
You might try (1) using twisted pair instead of zip line to your speakers and (2) using ferrite bead clamps, a few turns wrapped around both ends of the speaker cable. But it probably won't help, as it's likely your speakers internal amplifier is picking up the signals directly, as they're cheaply made (see TOA) and poorly shielded.
Re:Nothing to see here. (Score:3, Informative)
It's not a magnet. It's ferrite.
Re:Nothing to see here. (Score:5, Informative)
Not on 3G, EDGE only (Score:5, Informative)
Re:Americans should write to the FCC and complain (Score:3, Informative)
You don't quite understand the cause of the problem -- it's not that phones are transmitting on the wrong frequency or "splattering" the spectrum. It's that devices like unshielded speakers are prone to pick up interference like this from all across the spectrum, including the GSM bands.
Cell phone transmitters are much more heavily regulated than consumer electronics like clock radios.
Re:Nothing to see here. (Score:4, Informative)
SOS for the Morse intolerant.
Re:Nothing to see here. (Score:5, Informative)
They're a very simple passive device that works by disrupting high frequency RF passing through the cord. Since any large (long) conductor can function as an antenna, most cables are really just giant antenna, so adding a ferrite bead is a really cheap and simple way to counteract this. As for interference within a speaker itself (that is, not arriving by way of the speakerwire used to hook it up) there's not much you can do other than putting a Faraday cage around the speaker, or just moving the source of noise farther away from the speaker.
Re:FCC Rules Part 15 (Score:3, Informative)
Leighklotz is exactly right, but it gets even worse. Even a Part 15 device, using similar modulation to the GSM phone, could likely cause interference to your speakers. I have a DECT phone, compliant with FCC Part 15, sitting next to my computer speakers, and it creates a nice buzz when it's searching for the base. That's not the phone's fault, I'm sure they're transmitting all their energy in the allowed band, but nonetheless my speakers are rectifying that RF energy and amplifying the resulting envelope. The "device may not cause harmful interference" part of the Part 15 regulations refers specifically to spurious emissions outside the permitted band(s) of operation. Unfortunately, inexpensively made or carelessly designed electronics, which constitute the bulk of consumer offerings, often don't include much protection from interference. Regardless of whether the interfering device is operating properly or not, these devices will suffer.
Re:Psh (Score:5, Informative)
Re:Nothing to see here. (Score:3, Informative)
It's not so much the computer as it is the speakers themselves. The long cheap unshielded speaker wires pick up GSM interference, whose lower harmonics result in that distinctive buzzing sound. The speaker wire basically acts as an antenna.
Digital speakers obviously don't suffer from this phenomenon, but they're hard to find outside of pro-audio circles and the occasional cheapo USB speaker set.
Re:Psh (Score:3, Informative)
Except that when an Ipod (or other WSD) is broadcasting on channel 18, not all the signal stays inside channel 18. A lot of it spills-over into WPHL's channel 17. Think of them as the EM equivalent of harmonics of the original signal.
So you cannot place two broadcasts directly side-by-side and expect it to work. This is not a flaw of design. This is a flaw of nature. "You cannae change the laws of physics" is a favorite joke from Star Trek, but it also happens to be true. A DTV receiver cannot decode WPHL-17's signal when the Ipod/WSD on channel 18 is overflowing its own signal onto the channel.
Re:the cause could be put into the summary (Score:3, Informative)
So the poster is correct. It is a 217Hz RF pulse with about 500uS pulse width.
Cell phones use an electric field antenna which produces a high near field electric field that decays at 1/r cubed, and a propagating electromagnetic field that decays at 1/r.
It is most likely the near field electric field (capacitively coupled) that is consequently demodulated by any non linear components in your speaker amplifiers as the PA (Power Amplifier) in the phone changes power level.
Even though the electronics industry is one of the most regulated in the world with a zillion tests, there is no mandatory test for effects on electronics from near field coupling of transmitters such as mobile phones.
I had a product many years ago that passed all the regulatory tests, but would fail when put right up to a mobile phone. Adding a 47pF cap to the clk line an external EEPROM solved the problem.
Re:FCC Rules Part 15 (Score:3, Informative)
Your speakers have to live with it.
You might try (1) using twisted pair instead of zip line to your speakers and (2) using ferrite bead clamps, a few turns wrapped around both ends of the speaker cable. But it probably won't help, as it's likely your speakers internal amplifier is picking up the signals directly, as they're cheaply made (see TOA) and poorly shielded.
What will twisted pair do ? Doesn't twisted pair only protect against interference when you have a balanced line [wikipedia.org] with opposite voltages going down each wire?
Read this, page 2 [audiosystemsgroup.com]: