radio interference (OT)?

Has anyone else been hearing burst of digital chatter that
leak into 
audio systems and telephones from a strong interfering
signal? I've 
been hearing it at home for a month: a half-second burst
every 10 
miutes or so. There are no signals at all in the basement at
work...

-tc


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That's probably a GSM Cell phone, there is a particular
signaling 
protocol that induces audibly on unshielded audio inputs. 
It's 
basically an "I'm over here" signal that the phone
emits to the cell 
network periodically.  If you don't have any cell coverage
down there in 
the basement the phone is probably going to max power when
it emits it, 
in an attempt to reestablish contact with the network.  The
protocol 
(who's name I forget) was designed to maximize detectability
by the 
network with minimal power use. 

YMMV, since I can't hear what you're hearing. 

-J

Ted Crum wrote:
> Has anyone else been hearing burst of digital chatter
that leak into 
> audio systems and telephones from a strong interfering
signal? I've 
> been hearing it at home for a month: a half-second
burst every 10 
> miutes or so. There are no signals at all in the
basement at work...
>
> -tc
>
>
>
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-- 
Jay Bryon
Senior Network Engineer, U.C. Berkeley/IST/IS/NSO 
jayberkeley.edu
2-5636

"Any idiot can be complex, it takes real genius to be
simple"
-Al Einstein

[Unless stated explicitly otherwise, all opinions are my own
(or Al's) and do not represent official policy of any part
of IST, U.C. Berkeley or the U.C. Regents.]  



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Yes, another poster nailed the GSM phone. We had been a
peaceful, 2 
SprintPCS phone (CDMA 1900) until the bosses strapped a
Blackberry 
onto my wife.

BTW, I don't get noise in my basement (that's why it was a
bit OT); 
just me and my Sprint.


At 01:38 PM 10/9/2007, you wrote:
>I might venture to guess a cell phone is usually the
culprit in 
>these sort of cases.  PA systems are particularly
susceptible to the 
>rf from nearby cell phones.  A quick sequence of thumps
is often heard.
>
>In the basement of many of the campus buildings, it can
be difficult 
>to pick up even the many local high-power AM broadcast
stations, 
>much less cell phone 'pings'.
>
>That would be one candidate.  Can you localize the issue
to a building?  room?
>
>Wifi transmitters may also be getting into your
devices.
>
>Interesting issue.  recording the sound would help
identify the signal source.
>
>Thanks,
>        Jack Burris, K6JEB
>        SSCL
>
>
>Ted Crum wrote:
>>Has anyone else been hearing burst of digital
chatter that leak 
>>into audio systems and telephones from a strong
interfering signal? 
>>I've been hearing it at home for a month: a
half-second burst every 
>>10 miutes or so. There are no signals at all in the
basement at work...
>>-tc
>>
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Web site:
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on the Internet.
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others) your bosses,
>>prospective employers, and people who have known you
in the past.
>


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Oh, I just experienced another interference I previously
experienced that I
forgot about.  At least with my treo, it actually interferes
with my usb
mouse!  It only happens when the phone is sitting inches
away from the
mouse, but has happened to me on at least three separate
computers.  Took me
a while to realize why my window kept scrolling on its own.

But as far as I know, Verizon uses CDMA.  I do not know if
this issue exists
with CDMA to such degree.

Ted Crum wrote:
> Yes, the Wikipedia entry describes exactly what I am
experiencing. Blame
> the new UCSF Blackberry (Verizon) that my wife carries.
It must be a
> strong one; it gets the stereo from 8 ft away, through
a wall. Send in
> the Ferrites!
> 
> -tc
> 
> 
> At 01:21 PM 10/9/2007, John Kim wrote:
>> I think many people have experienced this.  Many
people know the "psychic"
>> phenomenon, where their speakers start making
slight noise a second or two
>> before their phone starts ringing.
>>
>> At least from my experience, Cingular network is
the biggest offender of
>> this.  I've been on T-Mobile, Sprint, and Cingular,
but no experience with
>> Verizon.  I think it may be the 900MHz frequency
that Cingular uses that
>> causes it more often than not.  I've switched from
T-Mobile, which at
>> least
>> back at the time only used the 1800MHz band, to
Cingular on the same exact
>> phone (unlocked) and noticed the difference almost
immediately.
>>
>> When I'm walking, I need to make sure to keep my
phone and my ipod on the
>> opposite sides to prevent interference.
>>
>> It is even mentioned in wikipedia, with the
obligatory [citation needed]
>> markups:
>>
>> http://en.wikipedia.org/wiki/Gsm#Interference_wi
th_audio_devices
>>
>> When I was with Sprint, I noticed only rare minor
interference, and only
>> when the phone was right next to a speaker.  But
this was back before the
>> days of UMTS and such features.
>>
>> Ted Crum wrote:
>> > Has anyone else been hearing burst of digital
chatter that leak into
>> > audio systems and telephones from a strong
interfering signal? I've been
>> > hearing it at home for a month: a half-second
burst every 10 miutes or
>> > so. There are no signals at all in the
basement at work...
>> >
>> > -tc
>> >
>> >
>> >
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>> > about upcoming meetings, please visit the
Micronet Web site:
>> >
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>> >
>> > Messages you send to this mailing list are
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>> > and the list's archives can be browsed and
searched on the Internet.
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>> > prospective employers, and people who have
known you in the past.
>>
>> -- 
>> John Kim
>> System and Network Security
>> http://security.berkeley
.edu

-- 
John Kim
System and Network Security
http://security.berkeley
.edu

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