cell phone intererence / feedback
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From: Charles on 12 Jan 2010 21:09 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(a)tpg.com.au> ���g��l��s�D:7r4ip7Fhk9U1(a)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 > > >
From: John Walliker on 13 Jan 2010 16:51 On 13 Jan, 02:09, "Charles" <wlchu...(a)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
From: John Walliker on 13 Jan 2010 16:55
On 12 Jan, 17:35, "Mike" <a7b98...(a)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 |