cell phone intererence / feedback
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From: Mike on 9 Jan 2010 02:18 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.
From: Phil Allison on 9 Jan 2010 08:32 "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
From: terryS on 10 Jan 2010 13:15 On Jan 9, 10:32 am, "Phil Allison" <phi...(a)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.
From: Mike on 12 Jan 2010 12:35 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(a)nf.sympatico.ca> wrote in message news:f41dab86-6bf3-40c7-bfad-9fc925f9eae9(a)f6g2000vbp.googlegroups.com... On Jan 9, 10:32 am, "Phil Allison" <phi...(a)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.
From: Phil Allison on 12 Jan 2010 19:34
"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 |