GSM-only interference [Telecom]

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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?

Re: [telecom] GSM-only interference [Telecom]
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.


Austin, Texas, USA

Re: GSM-only interference [Telecom]

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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.

"C'est un Nagra.  C'est suisse, et tres, tres precis."

Re: GSM-only interference [Telecom]

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

The only good spammer is a dead one!!  Have you hunted one down today?
(c) 2009 I Kill Spammers, inc, A Rot in Hell. Co.

Re: GSM-only interference [Telecom]
Thad Floryan wrote:

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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.


Re: GSM-only interference [Telecom]
On 8/7/2009 6:07 AM, Dave Garland wrote:
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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.).

Re: GSM-only interference [Telecom]
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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.

Re: GSM-only interference [Telecom]

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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
Avant de repondre, jeter la poubelle, SVP

Re: GSM-only interference [Telecom]

On 8/21/2009 6:53 AM, tlvp wrote:
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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.

Re: GSM-only interference [Telecom]

Thad Floryan wrote:


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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

Re: GSM-only interference [Telecom]

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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".

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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.

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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'.  :)

Re: GSM-only interference [Telecom]

On 8/22/2009 6:16 AM, Michael Grigoni wrote:
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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:

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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)).

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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

Re: GSM-only interference [Telecom]

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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

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 ( /) and research the literature
on RF shielding.

Bill Horne

Re: GSM-only interference [Telecom]

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*BINGO*  The signal pattern has an 'envelope' component that hits the
audio spectrum.

Better shielding of the 'affected' devices *IS* the answer.

Re: GSM-only interference [Telecom]

On 8/26/2009 8:17 PM, Robert Bonomi wrote:
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Just curious: how does one retrofit shielding into affeected hearing aids
and other implanted medical appliances as was mentioned in the 1994 article
from the comp.dcom.telecom archives and recently reposted by me?

Google search just now didn't find it, so I uploaded the article here:

< [7 KB]

The article claims GSM's interference problems were suppressed until after
GSM's rollout.

Re: GSM-only interference [Telecom]

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If the manufacturer didn't build the device correctly in the first place,
_who's_ fault is that?

FCC rules are _very_ explicit on the matter -- if a device is affected by
a _properly_operating_ transmitting device, the 'problem' *is* in the device
that is being affected.  

If the device isn't 'repairable', the option then is to _replace_ it with
one that is properly shielded.  It is solely the problem of the user of
the affected device.  So says the (*long* established) law.

Re: GSM-only interference [Telecom]

On 8/27/2009 11:28 AM, Robert Bonomi wrote:
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Per the information in the 1994 comp.dcom.telecom article, it can be
argued that GSM cell phones are inherently flawed. To wit (from the article):

"   1. General R/F pollution.  Any system that switches its R/F
"   transmitter on and off rapidly (GSM does it 217 times a second, TDMA
"   does it 50 times) will scatter EMI throughout the adjacent radio
"   spectrum.  And the sharper the edge of the switch power (on and off),
"   the wider the band of hash it scatters.  These sets need a 3-5MHz
"   guard-band between them and analog AMPS channels,and they try to ramp
"   up the power, and still they scatter crap into nearby television
"   broadcast bands. We've never had anything that generates EMI like a
"   GSM handset before in these bands.  We need large numbers of them like
"   we need a hole in the head.
"   2. Audio-Hz interference.  The on-off cycle of transmission power will
"   be read by any analog circuit nearby (with any rectification or
"   asymmetrical circuits) as an intrusive audio tone of 217Hz, and the
"   two major harmonics above.  This buzz intrudes into hearing aids at
"   distances up to 30 metres, and is often intolerable at 2 metres. It
"   also gets into cassette recorder, wireline systems, and into modems as
"   a carrier tone.

I don't see how anyone can justify the above two items as being "normal",
especially since a GSM cell phone can be transmitting at up to 2 Watts.

The 1994 article concluded:

"   The real problem with both GSM and American TDMA is the way in which
"   all these problems were kept secret, and the systems were rolled out
"   slowly and quietly without anyone admitting problems until the press
"   started shouting.  When they play these sorts of games, they have only
"   themselves to blame when the press reacts strongly and shouts 'foul'
"   especially when it is likely to be hearing-impaired people who suffer
"   in office environments.
"   Later, problems were reluctantly admitted, but always the admission
"   was associated with "Don't worry, well fix it!" which is just another
"   of their lies.  Most of these problems are intrinsic in time-division
"   power pulsing.
"   More recently the tactic has changed once again: now they blame the
"   lack of shielding on hearing-aids and other electronic equipment, and
"   want to boost the standard of immunity, rather than reduce their own
"   emissions.
"   It's the smoke-stack blaming inefficiencies in gas-masks for the
"   problems.  ETSI is its own worst enemy.

Are you disagreeing with the above?

Re: GSM-only interference [Telecom]

Thad Floryan wrote:

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Retrofitting to ameliorate poor design is difficult.  Implanted
medical devices are especially problematical.. you probably have seen
signs near microwaves, antitheft gates, etc. warning pacemaker users.
I suppose you could wrap yourself in aluminum foil, but that's not
attire suited for all social occasions.

Fortunately, cell phones don't seem to affect implanted hardware
much. It might be that the surrounding tissue provides shielding for
the implanted device, or maybe those devices are not actually very
sensitive to interference.


Re: GSM-only interference [Telecom]

Thad Floryan wrote:
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A number of years ago in Phoenix US West made us leave our cell phones
at the guard desk before we could get in.

The only good spammer is a dead one!!  Have you hunted one down today?
(c) 2009 I Kill Spammers, inc, A Rot in Hell. Co.

Re: GSM-only interference [Telecom]

On Sat, 22 Aug 2009 09:16:21 -0400, Michael Grigoni wrote: .....
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If a disease-carrying mosquito bites you on the face you will probably
feel it compared to if it bites you on the back, but you still have the
same chance of being affected/infected by the bite - it is just one area
of skin is more sensitive than the other.

If you notice a GSM phone interfering with something because of the
noticeable modulation pattern and you do not notice another type of
transmitter interfering with the exact same equipment because its
interference pattern is different, chances are the equipment is still
being affected by both devices - especially if the interfering power
levels and frequencies are similar.

Regards, David.

David Clayton
Melbourne, Victoria, Australia.
Knowledge is a measure of how many answers you have, intelligence is a
measure of how many questions you have.

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