a science related question

[bharat_r]

How do I hear noices in the speaker when I place my cell phone near it & I get a SMS or a call?

How does the interfirence take place?Can someone explain in a Physics point of view.

[tuxfan]

Those are the signal waves coming from the cell operator tower to your cell

[Vishal Gupta]

I also many times faced it.
Whenever my cellphone is near to the radio or TV, a strange sound( like beep) starts coming and I can know in advance that a new call or SMS is coming in a few seconds.


This problem seems to occur ,when recieving a page for an incoming call. Cell phones also cause the radar detector to go nuts.

[bharat_r]

So that's why they tell us to switch off cell phones on board airplanes.

If any one could find a a link or explain on their own how the cell phone's waves interfer with the speakers causing beeps.

[bharat_r]

So that's why they tell us to switch off cell phones on board airplanes.

If any one could find a a link or explain on their own how the cell phone's waves interfer with the speakers causing beeps.

[siriusb]

Mobile phones produces high energy waves for communication. The energy is enough to activate those tiny fancy lights that you can attach to the back of a mobile phone. But it decays inverse squarely so that on reaching the tower it is only enough to be heard.
I guess this wave is acting on the voice coils of ur speaker and producing currents which in turn is driving the speaker.
Call initialization can take a lot of energy, so you may actually see the interference in the crt monitors and speakers seconds before ur mobile phone starts to ring.

[siriusb]

Originally Posted by bharat_r

So that's why they tell us to switch off cell phones on board airplanes.

In airplanes, an unsheilded wire might get current when there should be no current in there if a mobile phone is place near it. But it has to be so close to the wire/equipment to start any serious damage.
But when airplane is so high in the air, ur cellphone tries to increase its power output to maximum. If all the passengers' cell phones did that, the airplane wud go haywire. Same thing is applicable to hospitals' icq (or something like that) rooms.

[siriusb]

Originally Posted by tuxfan

Those are the signal waves coming from the cell operator tower to your cell

It couldn't be the wave from the operator to ur cell, otherwise all the TVs, radio, etc in the city would go berserk.

[bharat_r]

siriusb,thanks for that info.

[bharat_r]

One more thing,does it damage the speakers?when I work on the comp I somtimes tend to keep the mobile next to my speakers.

[tuxfan]

Originally Posted by siriusb

It couldn't be the wave from the operator to ur cell, otherwise all the TVs, radio, etc in the city would go berserk.

Pardon my non-techie jargaon. But whatever way you put it, it ultimately remains the signal waves from here to there.

[pradeep_chauhan]

The noise or interference we here in the speakers / TV / Stereo is from the transmissions made from the hadset that are placed next to these devices. The signal originating from the cell is strong and its harmonics create the strange beeps we here. Also these noise are due to the transmissions from the cell phone rather than the tower as the signal strength is much higher as compared to the transmissions made from the tower/BTS.

[huzaifa b arab]

I think it's due to the similarityies in the signal frequencies whichm disturbs everything....

[kalpik]

Hmm one point id like to clear, a cell phone wave's power is not enough to induce current in the speaker. Actually, it does not interfear wid the speaker at all! It interfears wid the electronics. There are two types of cellphones used in India: GSM and CDMA. As u all must have noticed, nothing is disturbed when u get an incoming call on a CDMA Phone, only the GSM phone interfears. GSM allots a different frequency to each subscriber to differentiate btw different subscribers. When not in use (as in just switched on and standby) to save battery power, the phone is not in contact wid the tower (that is why if the phone is in standby, and u remove the batt widout switching off, the phone becomes unreachable instead of showing switched off). So whenever the tower gets the call or an SMS, it sends an ENABLE signal to the frequency of the cell phone concerned. The cell phone then "Handshakes" wid the tower by returning the signal (This is the signal that creates the beeps). When the signal reaches the tower, the call is established (Thats why it takes a few secs before the phone rings) And if the signal is NOT returned by the mobile, it is rendered not reachable. When u switch off ur phone, it sends another signal to the tower, signalling that it has been switched off (So the tower does not waste time searching). That is how a GSM mobile works.

Whew! Long post, hey but remember, dont ask for source, cuz i wrote each n every word myself! Hehe

[kalpik]

Here's how CDMA works. Hehe!

CDMA allots the same frequency to many phones, only the information transfered is encoded, and only the correct phone can decode it. It operates on some frequencies (dunno exactly) but it does not interfear wid electronic items (hence no disturbance to other electronic items). One thing though, CDMA waves have "Scrambling" effect. Try this: take a cheap quality FM radio, tune it to some frequency (so that u can hear a particular channel) then take a CDMA phone near it, and make a call. The FM radio will stop working and u wil have to re-tune it. Hehe.

[expertno.1]

if i keep my mobile near my monitor..it vibrates....why ? give ve me physics point of view

[pimpom]

This thread has been going on longer than I thought it would.
A short answer to the OP's question would be that radio (electromagnetic) waves radiating from the phone is causing interference with the computer's audio system. But that's fairly obvious.

The problem with trying to give a more detailed explanation is that we have to go into electronics in some depth and that may not be very appropriate for this forum. It may also not be very helpful to someone without some background in electronics. Let's see what we can do without invoking too much technical jargon.

Someone else has already stated that it must be the response signal from the phone and not the signal from the tower that's causing the interference. That's true. Under normal circumstances, the signal from the tower is too weak to cause interference. The signal from the phone is also too weak to directly cause the speaker to vibrate unless perhaps it's placed very close to the voice coil.

Most electronic circuits involve amplification, that is, a weak voltage or current goes into one end (input) and a stronger version of that voltage/current comes out at the other end (output). Any fluctuation at the input comes out as a much stronger fluctuation at the output. In many cases, the fluctuation is intentional and carries meaningful information or data.

After the signal has gone through enough amplification, it is made to go through a non-linear section that extracts the information carried. This is called "detection". This process of amplification and detection takes place inside a radio, TV or cellphone.

But sometimes the amplification-detection process is accidental. The signal from the phone induces a current in some part of the audio system's amplification chain. It gets amplified and detected and finally emerges as sound from the speaker.

@expertno.1 : when you say "it vibrates", do you mean the mobile or the monitor display ?

[raasm287]

coz the speaker is interpreting the radio waves.

[nirubhai]

These problems are common in GSM & TDMA systems.
Here are some exrepts i found on the net.

GSM data bursts are at 217 Hz which is in the range of human hearing.
The noise coming through the speakers is due to the GSM signalling, particularly on 850mhz systems.

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.

This buzz intrudes into hearing aids at distances up to 30 metres, and is often intolerable at 2 metres.

I just have to make sure that the phone is at least 3 feet away from the speakers to minimize (note it does not eleminate it) what is coming over them.

It ain't the speakers - it's the unshielded wires connecting the speakers to the amplifier equipment that pick up the interference.
You can prevent that interference by using coaxial cables for the speaker wires.
Aside from that, the only other thing that can be done is physical separation of more than a few feet.
Most cell phone wired headsets have a filter circuit embedded in the headset jack and blue tooth headsets don't need it.

Some Links
Health Physics Society: Cellular Phone and Base Station
How Stuff Works: I've noticed that I am not allowed to use my cell phone in airplanes or in hospitals. Why are these prohibitions in place?
PDF: Fundamentals of Interference in Wireless Networks (This has the physics )
PRIVATE LAND MOBILE INTERFERENCE COMPLAINTS (just in case you need it)
Moto V551: hourly interference with computer speakers? (a long mailing list. you will need patiance to read. but worth reading)

[navjotjsingh]

Is any mod looking here. Almost all users have posted more than one times in succession. Why can' they edit their posts. that's how their post counts are so large.

[vinayasurya]

Why they ask to switch off mobile phones at fuel stations?