cell phone intererence / feedback

[Mike]

Hi There,

Can someone explain to me why whenever my GSM cell phone rings, I hear that
humming/pulsing sound on any audio equipment that's near the phone such as
an MP3 player and a set of ear buds. Why would GSM transmissions on
800/900MHz or even 1.9GHz create that audio pulsing sound within the
baseband audio spectrum which I subsequently hear using my ears buds near
the phone?

thanks Mike.

 

[Phil Allison]

"Mike"

Can someone explain to me why whenever my GSM cell phone rings, I hear
that humming/pulsing sound on any audio equipment that's near the phone
such as an MP3 player and a set of ear buds. Why would GSM transmissions
on 800/900MHz or even 1.9GHz create that audio pulsing sound within the
baseband audio spectrum which I subsequently hear using my ears buds near
the phone?

** Because GSM phone signals are continuously, 100%, amplitude modulated at
an audio frequency.

Circa 270Hz - IIRC.

Scientifically engineered to break into every damn audio device ever built.

Soon may it die.



.... Phil

 

[terryS]

On Jan 9, 10:32 am, "Phil Allison" <phi...@tpg.com.au> wrote:

"Mike"



Can someone explain to me why whenever my GSM cell phone rings, I hear
that humming/pulsing sound on any audio equipment that's near the phone
such as an MP3 player and a set of ear buds.  Why would GSM transmissions
on 800/900MHz or even 1.9GHz create that audio pulsing sound within the
baseband audio spectrum which I subsequently hear using my ears buds near
the phone?

** Because GSM phone signals are continuously, 100%, amplitude modulated at
an audio frequency.

 Circa  270Hz   -   IIRC.

 Scientifically engineered to break into every damn audio device ever built.

 Soon may it die.

...  Phil

Many electronic devices, built to be sold at competitive prices, even
expensive audio gear, will not reject relatively strong RF (Radio
Frequency) from close by. These unwanted and unexpected radio signals
can overload an electronic circuit and any content/modulation may then
be imposed (added) onto whatever signal the electronic equipment is
handling.

My particular story is about a NATO radar pulse (many gigahertz?) that
clicked at every rotation of the antenna when my car radio was tuned
to a radio station at around 600 kilohertz. The radar pulse must have
been relatively so strong that it overloaded the car radio every time
it pulsed in my direction.

 

[Mike]

Thank you for the replies.

What's interesting is that I generally (IIRC) only hear the initial ring
tone associating with an incoming call and periodically during non-active
intervals when the handset is communicating with the network but no active
call is in place. So in GSM based systems, is the ringing tone actually
modulating the RF wideband carrier (TDMA-based) and hence the ringing tone
which is audible in the audio band, is superimposed on my MP3 player
headphones to which the 3' cabled connection acts as a receiving antenna?
Or since GSM is a digital system, I am merely hearing the "digital" pulsing
sounds of an incoming call which is a digital command from the network
indicating an incoming call and instructing the phone to play the audible
ring tone.

Do CDMA-based phones exhibit similar behavior?


"terryS" <tsanford@nf.sympatico.ca> wrote in message
news:f41dab86-6bf3-40c7-bfad-9fc925f9eae9@f6g2000vbp.googlegroups.com...
On Jan 9, 10:32 am, "Phil Allison" <phi...@tpg.com.au> wrote:

"Mike"



Can someone explain to me why whenever my GSM cell phone rings, I hear
that humming/pulsing sound on any audio equipment that's near the phone
such as an MP3 player and a set of ear buds. Why would GSM transmissions
on 800/900MHz or even 1.9GHz create that audio pulsing sound within the
baseband audio spectrum which I subsequently hear using my ears buds
near
the phone?

** Because GSM phone signals are continuously, 100%, amplitude modulated
at
an audio frequency.

Circa 270Hz - IIRC.

Scientifically engineered to break into every damn audio device ever
built.

Soon may it die.

... Phil

Many electronic devices, built to be sold at competitive prices, even
expensive audio gear, will not reject relatively strong RF (Radio
Frequency) from close by. These unwanted and unexpected radio signals
can overload an electronic circuit and any content/modulation may then
be imposed (added) onto whatever signal the electronic equipment is
handling.

My particular story is about a NATO radar pulse (many gigahertz?) that
clicked at every rotation of the antenna when my car radio was tuned
to a radio station at around 600 kilohertz. The radar pulse must have
been relatively so strong that it overloaded the car radio every time
it pulsed in my direction.

 

[Phil Allison]

"Mike"

What's interesting is that I generally (IIRC) only hear the initial ring
tone associating with an incoming call and periodically during non-active
intervals when the handset is communicating with the network but no active
call is in place. So in GSM based systems, is the ringing tone actually
modulating the RF wideband carrier (TDMA-based) and hence the ringing tone
which is audible in the audio band, is superimposed on my MP3 player
headphones to which the 3' cabled connection acts as a receiving antenna?
Or since GSM is a digital system, I am merely hearing the "digital"
pulsing sounds of an incoming call which is a digital command from the
network indicating an incoming call and instructing the phone to play the
audible ring tone.

** The only GSM signals you hear on audio devices come only from *nearby
phones* - you do not hear any of the transmissions from base stations.

When a GSM phone receives a call from a base station, it responds with an
acknowledgment transmission - which you may hear on your MP3 player.

The ring tone is generated inside the phone and you hear this with your
ars - direct.

During a conversation, a GSM phone transmits digital data in a stream of
short bursts, 217 of them per second. It is not possible to hear any of the
actual data on audio devices. The *pattern* of the data bursts is what you
hear as buzzing noise.

The RF energy in each ( millisecond long) burst causes a tiny change in the
operating level of a transistor or IC inside the audio device, at the end of
the burst the operating level returns to normal thus generating an audio
frequency signal at the burst repetition rate of 217 Hz.



..... Phil

 

[Charles]

Dear sirs,

It's very annoying to hear this noise whenever listening to the music by the
speaker,

I would like to know if any simple circuitry that could filter out these
noise generated

by the GSM phone signal.

Any idea or reference? Thank you very much.

(I am quite new to this forum...)


"Phil Allison" <phil_a@tpg.com.au> źśźgŠóślĽóˇsťD:7r4ip7Fhk9U1@mid.individual.net...

"Mike"

What's interesting is that I generally (IIRC) only hear the initial ring
tone associating with an incoming call and periodically during non-active
intervals when the handset is communicating with the network but no
active call is in place. So in GSM based systems, is the ringing tone
actually modulating the RF wideband carrier (TDMA-based) and hence the
ringing tone which is audible in the audio band, is superimposed on my
MP3 player headphones to which the 3' cabled connection acts as a
receiving antenna? Or since GSM is a digital system, I am merely hearing
the "digital" pulsing sounds of an incoming call which is a digital
command from the network indicating an incoming call and instructing the
phone to play the audible ring tone.


** The only GSM signals you hear on audio devices come only from *nearby
phones* - you do not hear any of the transmissions from base stations.

When a GSM phone receives a call from a base station, it responds with an
acknowledgment transmission - which you may hear on your MP3 player.

The ring tone is generated inside the phone and you hear this with your
ars - direct.

During a conversation, a GSM phone transmits digital data in a stream of
short bursts, 217 of them per second. It is not possible to hear any of
the actual data on audio devices. The *pattern* of the data bursts is what
you hear as buzzing noise.

The RF energy in each ( millisecond long) burst causes a tiny change in
the operating level of a transistor or IC inside the audio device, at the
end of the burst the operating level returns to normal thus generating an
audio frequency signal at the burst repetition rate of 217 Hz.



.... Phil

 

[John Walliker]

On 13 Jan, 02:09, "Charles" <wlchu...@gmail.com> wrote:

I would like to know if any simple circuitry that could filter out these
noise generated

by the GSM phone signal.

Any idea or reference?  Thank you very much.

Unfortunately, there is no simple filter which will remove GSM
interference. It would be difficult - perhaps impossible - to do even
with a complex filter.

John

 

[John Walliker]

On 12 Jan, 17:35, "Mike" <a7b98...@telus.net> wrote:

What's interesting is that I generally (IIRC) only hear the initial ring
tone associating with an incoming call and periodically during non-active
intervals when the handset is communicating with the network but no active
call is in place.

At the beginning of a call - during ringing if it is an incoming call
- the phone transmits at full power. After a few seconds the base
station reports signal strength information back to the phone which
will cause it to reduce transmit power if the base station is nearby.
The reduced power may be low enough not to interfere with your audio
equipment.

John