GSM-only interference [Telecom]

I searched this group for "GSM interference" within Google Groups and found nothing, so this may be "something new" for some readers.

Yesterday, after a lunch meeting with a Nokia guru, we adjourned to my home office to review some matters and, within seconds of booting one of my systems, a "noise problem" that has sort-of bugged me for a year evidenced itself. The Nokia guru instantly stated that sound was GSM interference.

I was both relieved and puzzled; my cell phone is a Motorola RAZR V3.

Relieved because I now knew for certain the "sound" wasn't a virus or other malware. My concern began last year when I first heard a "dit-dit-dit dit-dit-dit dit-dit-dit dit-dit-dit" and thought some malware had somehow arrived on my system. Using Process Explorer and several AV scans revealed nothing, and since the sound only appeared no more than once or twice every day and then only for a second or two, I tolerated it.

Puzzled because the Nokia guru stated this was a common and known problem. So bad that in fact at Nokia HQ they turn off all the Polycomm conference room phones when having a meeting; he stated also that Polycomm phones are the worst offender in this regards.

Later I did a normal Google search using "GSM interference" and, WHOA!, 1000s of pages of hits. Many affecting pro audio studios' sound mixing consoles. Long story short, this "GSM inteference" appears to be a widespread problem and it's only with GSM, not any of the other cell phone or PDA technologies.

To hear the sound I'm talking about (just a few seconds each):


Here's one explanation for the sound which I found here:

" If you ever do any type of recording or use devices with " audio components the day will come where you hear this " awful racket. Some call it buzz, some say it sounds like " a fax machine and others call it things I won't print here. " It sounds like this. What is that noise? It's a BlackBerry® " type device or an iPhone (GSM) checking in with master " control. It is the sound of digital data being transmitted. " At very low levels (when the phone is some distance away), " the "buzz" may not be heard, but your audio will sound like " there's some "fuzz" on it. The guilty device can be anywhere " in the room, possibly passing in the hallway or all the way " across the lobby. It is imperative that you monitor your " recording because you never know when the problem will occur. " " What can you do about it? " Have the device turned OFF. Not on silent or vibrate but OFF. " If the device must remain on, then create as much distance " between the device and the audio equipment. The greater the " distance, the softer the interference. " " Cellular phones (GSM , TDMA), iPhones, or a BlackBerry® and " the like send out strong electromagnetic (EM) pulses as data " messages. They check in with the network for messages and to " report their location. CDMA phones and BlackBerry® devices " (Verizon) usually do NOT cause any problems.

So, how did GSM ever get FCC approval given this very widespread RFI/EMI problem?

Reply to
Thad Floryan
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I have a friend back in Atlanta who's a pretty straight-shooters. I don't think he was making this up. He placed his GSM phone on his paper shredder to charge as his cord wasn't long enough to reach anything else. His paper shredder kept turning on and then off all by itself. He moved the phone and it stopped.


Reply to
John Mayson

I wouldn't doubt it. It's pretty obvious with my computer. If I set my cell phone (either a Nokia or a Motorola) right by the computer, I can hear periodic bursts of noise from the speaker. Turn the cell phone off, or move it away, no more bursts.

I wouldn't blame the phone so much as the computer. The phone, after all, has to talk to the tower by radio periodically. And when GSM was designed, computers mostly didn't have audio, and were a lot better shielded than they are today. (Monitors, however were quite susceptible to interference from nearby fluorescent lights.) The computer manufacturers could shield things well enough so the interference wouldn't occur, but it would cost more, so they don't bother.


Reply to
Dave Garland

On Fri, 07 Aug 2009 00:06:01 -0400, Thad Floryan wrote: .........

The problem is not the GSM devices, it is in the receiving devices. If they can be interfered with by GSM frequencies then they can be interfered with by any other transmitter using those frequencies.

It is the nature of the GSM modulation that makes it more apparent in these devices. The devices themselves will be just as susceptible to other RFI/EMI sources, but because of the different modulation *you* may not notice it in the same way as with a GSM device.

The devices could actually be affected in a worse way as far as operating correctly goes by non-GSM transmitters, but the humans nearby may not notice that interference as readily as with the obvious effect GSM has, so it may well be worse to *not* know that a device is susceptible to interference!

Reply to
David Clayton

The more I think about it, it's not the computers per se but the external audio system with its unshielded cabling, plastic cases, etc. similar to the 10-second video here whose sound exactly matches what I hear except I get only four repetitions of the "dit-dit-dit" and not the 10 or so in that video.

Some 20+ years ago when the computers I ran at home 24/7 were Suns, AT&Ts, Convergents, etc., the FM radio in my car wouldn't function until I backed the car out of the garage.

The systems I operate today in my home office are actually well shielded and don't affect any of my radios but they do have audio outputs and that, I believe, is what the "GSM interference" is perturbing. It was July 2008 when I finally added an audio system (Altec Lansing with subwoofer) that the GSM interference became noticeable.

The question remains: why are only GSM phones causing the problem? The articles I found during yesterday's Google search universally claimed it's only GSM phones that affect audio systems (computer, mixing panels, recording studios, etc.).

Reply to
Thad Floryan

Makes sense. Thank you!

This is now starting to explain the reason "Why?" I was instructed to turn off my cell phone whenever I'd be working in a building's phone/wiring closet. At one client's site the building manager claimed cell phones would set off the fire alarms. Some times I'd forget to turn off my cell phone and I suppose I lucked-out the alarms didn't go off! :-)

But the finger is pointing at GSM as the culprit. Though I realize the GSM interference isn't a life-threatening situation (hmmm, what about being in a hospital?), I thought consumer appliances are not supposed to be causing such interference.

In any event, I was relieved to learn yesterday the sounds I was hearing were not the result of malware in my computers.

Reply to
Thad Floryan

Yes, that's the sound of a GSM phone talking to the tower. If I put my mobile next to my landline phone or the wire from the computer to the speakers, I can easily hear it.

R's, John

Reply to
John Levine

The answer to that gets _complicated_. But it boils down to the fact that it _isn't_ only GSM transmissions that get picked up. It is just an 'artifact' of the way the signalling for GSM occurs (timing, packet lengths, etc.) that picked up and rectified at a diode interface, ends up in the audible spectrum.

The GSM devices are working properly. They are not producing 'spurious' (off frequency) signals, or anything else inappropriate.

The problem lies in the _affected_ systems -- inadequate shielding, use of 'unbalanced' audio signals, etc. The 'problem' has been around for a _long_ time -- "long ago", I once had to 'fix' a church PA system that was picking up passing C.B. radio transmissions. And practically _every_ ham operator on HF can tell 'war stories' about 'unintended' reception by neighbors.

The _big_ difference today, is the sheer _number_ of such transmitters, and the *proximity* of the transmitter to the 'affected' equipment. that last, 'proximity', has a tremendous effect on the likelihood of pick-up -- a 100mw transmitter at 3 ft. is roughly the equivalent of a kilowatt transmitter at 300 ft. Make it 1-2", like the case mentioned in the other item, where the phone was sitting _on_ the paper shredder it was affecting, and the 'effective' power is _another_ several hundred(!!) times higher.

Reply to
Robert Bonomi

It isn't just the GSM phones that do this. Verizon was still using CDMA and my phone would do the same dit-dit-dit thing when a call was coming in.

People were surprised when I'd pick up before it even rang.

Reply to

That sounds like lousy shredder controller design as WELL as the usual nightmare that GSM cellphones cause with induced noise. But it doesn't surprise me a bit.

Turn the cellphone off, please.


Reply to
Scott Dorsey

On the news today they talked about a broiler turning on when he placed his cell phone on a counter near his stove.

Reply to

Thad, in my admittedly very limited experience, I hear these dit-dit-ta-dit's on nearby audio *only* when (a) I'm actively using my GSM phone's WAP browser, and a new deck is loading in response to my actions, (b) a fresh SMS message is coming in, or (c) I'm receiving an OTA update (variation on theme (b), I s'pose).

But what do I know? I just use the darn things, and put up with their foibles.

Cheers, -- tlvp

Reply to

In my town of Pahrump, NV, there is a local TV channel which has local live call-in talk shows for two hours every evening on various topics. Almost every night, I hear rat-a-tat bursts in the station's audio. When they occur, they repeat every 10 minutes or so. Most likely this is interference from cell phones in the pockets of the shows' participants.

Reply to

Even though I now know it's the phone causing the "dit-dit-dit dit-dit-dit ,,," on the computers' audio, I'm becoming concerned.

I used to have the phone (Motorola RAZR V3) on my belt while sitting at the keyboard in this setup . The audio stuff is 2-3 feet on the other side of that LCD monitor, 4 to 5 feet from me.

Since the Nokia guy stated it's GSM interference a few weeks ago, I've been taking the phone off my belt and placing it on a table 10 feet away. It still perturbs the audio with the "dit-dit-dit ..." several times a day and, just a moment ago when someone called. it totally swamped the computer audio with a loud buzzing hum just prior to the phone ringing.

I suppose the next test is to place the phone 30 feet away alongside a glass of water and see if the water boils when the GSM interference occurs. :-) I know that's absurd, but, still, the GSM interference I'm encountering is clearly a strong signal and some of the other anecdotes in this thread are disturbing; the one about the stove top turning on "by itself" suggests the GSM interference could be a fire and safety threat, and that elevates the severity of the problem to a whole new level.

What's odd is that I frequently use the phone while sitting at the keyboard and there's no disturbance to the computer audio whatsoever, so it seems the specific GSM interference symptom (the "dit-dit-dit ...") is either at a different frequency and/or power level than the phone in normal usage.

Reply to
Thad Floryan

I wonder if GSM phones create an increased danger of ignition of nearby flammables or of trigging of blasting fuses vs. AMPS or other phones; has anyone heard of a confirmed incident of such ignitions?


***** Moderator's Note *****

I wonder if the sky is falling.

Bill Horne

Reply to
Michael Grigoni

It's a complex situation -- depends on how badly shielded the computer audio is, and -where- you've got a 'dirty' connection acting as a diode/rectifier for the RF. Also, on how far away the cell tower is, and how much 'shielding' there is between you and the tower. The more 'stuff' there is between you and the tower, the higher the transmit power the phone has to use, to give a 'good' signal at the tower. Yes, the tower tells the phone to increase/decrease it's transmit power, as needed. Similarly, the phone advises the tower to change _its_ power level.

No chance of that, as I'm sure you know.

Well if you consider a few tens to a few hundreds of _milliwatts_ 'strong', then "yes, it's strong." "Legal limit" for transmit power for a U.S. GSM phone is 2 watts -- _most_ U.S. phones max out at 300-600 milliwatts. (limiting the max transmit power that way does wonders for extending battery run time. :)

It's _not_ a problem with the phone. It's *BAD*SHIELDING* in the affected device.

_Everything_ is in the _pattern_ of the data being transmitted. If the pattern happens to lie in the audio spectrum, *AND* a _badly-shielded_ device is nearby, you'll hear it. If the data pattern does _not_ give an audio wave- form, you won't hear it. If the device is adequately shielded, it won't pick up the signal, audio-spectrum or otherwise.

Based on my experience, the data pattern that tends to be the audible "did-dit-dit" one _appears_ to be a 'keep alive' type signal, where the cell system is checking to see 'if'/'where' the phone is still on the network.

Reply to
Robert Bonomi

Short answer, "No." GSM phones (at max legal power) are considerably lower power than 'normal' AMPS phones. GSM phones aren't transmitting with enough difference in power vs other U.S. cell technologies to make an _appreciable_ difference. Yes the *theoretical* range of such an effect is a _little_ (as in measured in feet) larger, but, as a practical matter that _slightly_larger_ range is "insignificant".

To my knowledge, there has never been a confirmed case of RF radiation from a cell phone igniting 'nearby flammables' of any sort. It takes a *VERY* SPECIAL set of circumstances for that to happen. A much larger (i.e., "higher probability") risk is that flammable _vapors_ get into the phone, and are set off by an arc across a make/break switch contact. And I don't think I've ever heard of -that- happening, either.

Not this time of year, around here. It just springs leaks. And it seems like "outside maintenance" has a very difficult time doing reliable repairs.

Give it another 5-6 months, and all these itty-bitty white pieces of the (overcast) sky *do* tend to start falling. Re-assembling all those little pieces is a *real* b*tch, not to mention getting them back 'upstairs'. :)

Reply to
Robert Bonomi

As I wrote previously in a different thread, one site where I worked for a number of years prohibited use of cell phones in the complexes' wiring closets due to the fire alarms going off. I never had that happen even while (forgetting and) using my cell phone in the closets; however, I seldom was in the closets for long and I doubt the specific instance of the GSM interference (the "dit-dit-dit ...") occurred while I was in the closets given it seems to happen only 3 or 4 times at day in my office.

However, as we've read already in this thread:

"Steven " wrote Aug. 18:

That broiler incident is what caused me to write yesterday there's a possible fire/safety issue with GSM phones.

As the 1994 article in the "post from the past" also stated, it's very difficult to reproduce these kinds of problems on demand with GSM phones since the blast of interference occurs randomly in my experience (3 or 4 times a day and never at the same times of day (and my phone is never turned off)).

Not in the "Chicken Little" sense, but I do believe we have several credible instances of GSM phones causing problems: turning on fire alarms, turning on/off a shredder, turning on a stove broiler, and

15 years of severe interference to professional audio mixing consoles and related gear.

It would appear to have reached the point it's worth investigating further; any ideas how to proceed?

***** Moderator's Note *****

Start by measuring the near-field RF strengh from a representative sample of cell phones, and determine if GSM power levels are significantly higher than TDMA, CDMA, or AMPS.

Assuming the answer is "yes", take steps to isolate RF-sensitive devices from the phones.

Bill Horne

Reply to
Thad Floryan

I understand (having designed/manufactured devices requiring FCC certification).

But given the 1994 comp.dcom.telecom article I recently reposted here and the numerous anecdotes of GSM-phone-caused problems. it seems the GSM phones, and only the GSM phones, are leaving a smoking gun trail everywhere. The 1994 article described several serious design faults all of which cause GSM phones to splatter noise across the airwaves.

It can be reasonably argued GSM should have never been approved for use given what I've been finding and discovering the past few weeks.

That seems a reasonable explanation and consistent with my usage; thank you!

Reply to
Thad Floryan

I don't seem to have seen this mentioned earlier in the thread (if I missed it, apologies...) but there's one key difference in GSM as opposed to the older analog system.

GSM utilizes time slots, hence there's more of a peaking effect in the emitted radiation. This can easily lead to different effects.

As an analogy, take a glance at a 25 watt regular incandescent. No problems looking, or even staring, at it.

On the other hand take a photoflash unit that stores up that electricity, then releases it as a single, short, and very intense strobe flash every couple of seconds.

The total energy per hour will be the same. But the strobe unit is much more annoying, in just about every sense of the term.

-- _____________________________________________________ Knowledge may be power, but communications is the key [to foil spammers, my address has been double rot-13 encoded]

****** Moderator's Note *****

You could measure either average or peak power density; the question is "Is GSM more likely to cause interference to audio devices, and if so, why?"

It may be that GSM signals are clocked at an audible rate, so that devices that aren't shielded are creating audible signals.

It may be that GSM signals from some phones exceed power limits in some cases.

It's possible that there is a mixing process at fault, and that the GSM transmissions mix with other signals to create broadcast-band interference.

No matter the cause, the fact remains that the vast majority of consumer-grade electronic devices do not have adequate RF shielding. There are a number of steps that users may take to reduce or eliminate interference, but the process is time-consuming and likely to need several rounds of experimentation before a solution is found. Readers who need help in this area should contact the American Radio Relay League

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and research the literature on RF shielding.

Bill Horne

Reply to
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