wtf is it with my cell phone

[eflat]

ever since i got this phone, any time i leave it by a speaker it causes interference. what is going on?

moving this to the phone and gadget forum -Anandtech Moderator DrPizza

 

[AMDMaddness]

totaly normal, I take it your phone is a GSM phone?

Pete

 

[newb111]

I've had that with any GSM phone I've ever had.

 

[Wonderful Pork]

as the posters above said, this is a GSM phenomenon called "GSM Buzz", it has to do with the time-division muliplexing of the GSM signal to your phone. It basically occurs when the phone's transmitter is turned on, which it isn't all the time for GSM, as opposed to CDMA where it is. This is why CDMS battery life is generally shorter. It is picked up by speakers and telephones because its at 200MHz or something, which is audible to the human ear.

It happens to me at work when my iPhone is close to my landline, i get this buzz through the earpiece from time to time.

You can't really prevent it unless you switch to CDMA, or you put the phone into Airplane mode (which is what I do)

 

[pm]

As a point of clarification, humans can't hear 200MHz. About the highest pitch that people can hear is 22-24kHz. Everything else you wrote, Mr. Pork, is dead-on though.

The underlying cause of the speaker noise is caused by the time division multiplexing technique used in GSM/TDMA. GSM uses time slots in the data stream that are dedicated to a given phone. As the phone enters a timeslot, interferance is created at frequencies that correspond to the length of the timeslot. There's a technical name for this that I can't remember (college was too long ago) but basically it's spectrum noise that gets picked up by unshielded devices that are nearby.

It can be prevented by turning off the transmitter (airplane mode, or turning it off), or by shielding everything (which is the technique used by Apple with "certified iPhone acessories"), or by creating a common ground plane between the devices - like the speaker/phone and the cell phone (also used by Apple with the iPhone). It can also be prevented by moving the cell phone away from the speaker... the power of a signal drops off by the cube root of the distance... so moving it a bit further away should dramatically reducing the noise.


As mentioned CDMA phones don't experience this problem (Verizon, Sprint, Cricket, etc.).

Also, nearly all of the "next generation" cell phone systems planned will not have this problem any more since every one that I can think of is moving over to a CDMA/W-CDMA/SOFDMA, OFDM and other code-based and frequency-based multiplexing schemes. Even similar schemes like TD-CMDA do not suffer from interference like TDMA/GSM.

 

[Wonderful Pork]

Originally posted by: pm
As a point of clarification, humans can't hear 200MHz. About the highest pitch that people can hear is 22-24kHz. Everything else you wrote, Mr. Pork, is dead-on though.

The underlying cause of the speaker noise is caused by the time division multiplexing technique used in GSM/TDMA. GSM uses time slots in the data stream that are dedicated to a given phone. As the phone enters a timeslot, interferance is created at frequencies that correspond to the length of the timeslot. There's a technical name for this that I can't remember (college was too long ago) but basically it's spectrum noise that gets picked up by unshielded devices that are nearby.

It can be prevented by turning off the transmitter (airplane mode, or turning it off), or by shielding everything (which is the technique used by Apple with "certified iPhone acessories"), or by creating a common ground plane between the devices - like the speaker/phone and the cell phone (also used by Apple with the iPhone). It can also be prevented by moving the cell phone away from the speaker... the power of a signal drops off by the cube root of the distance... so moving it a bit further away should dramatically reducing the noise.


As mentioned CDMA phones don't experience this problem (Verizon, Sprint, Cricket, etc.).

Also, nearly all of the "next generation" cell phone systems planned will not have this problem any more since every one that I can think of is moving over to a CDMA/W-CDMA/SOFDMA, OFDM and other code-based and frequency-based multiplexing schemes. Even similar schemes like TD-CMDA do not suffer from interference like TDMA/GSM.

Yea, I may have been slightly under the influence of a couple brews when I wrote that 200MHz part...good catch.

 

[mwmorph]

Originally posted by: pm
As a point of clarification, humans can't hear 200MHz. About the highest pitch that people can hear is 22-24kHz. Everything else you wrote, Mr. Pork, is dead-on though.

The underlying cause of the speaker noise is caused by the time division multiplexing technique used in GSM/TDMA. GSM uses time slots in the data stream that are dedicated to a given phone. As the phone enters a timeslot, interferance is created at frequencies that correspond to the length of the timeslot. There's a technical name for this that I can't remember (college was too long ago) but basically it's spectrum noise that gets picked up by unshielded devices that are nearby.

It can be prevented by turning off the transmitter (airplane mode, or turning it off), or by shielding everything (which is the technique used by Apple with "certified iPhone acessories"), or by creating a common ground plane between the devices - like the speaker/phone and the cell phone (also used by Apple with the iPhone). It can also be prevented by moving the cell phone away from the speaker... the power of a signal drops off by the cube root of the distance... so moving it a bit further away should dramatically reducing the noise.


As mentioned CDMA phones don't experience this problem (Verizon, Sprint, Cricket, etc.).

Also, nearly all of the "next generation" cell phone systems planned will not have this problem any more since every one that I can think of is moving over to a CDMA/W-CDMA/SOFDMA, OFDM and other code-based and frequency-based multiplexing schemes. Even similar schemes like TD-CMDA do not suffer from interference like TDMA/GSM.

I did noy know the industry was moving away from GSM. Does this mean Sim cards will no longer work and getting a new phone will be a new PITA when transferring over contacts?

 

[pm]

I did noy know the industry was moving away from GSM. Does this mean Sim cards will no longer work and getting a new phone will be a new PITA when transferring over contacts?

Third generation cellular systems (3G) nearly all use some form of CDMA (usually W-CDMA). The industry worldwide (and to some extent in the US) is using UMTS (also called 3GSM) for implementation of high-speed 3G networks. UMTS is not compatible with GSM at the air interface level, but a lot of the infrastructure is the same so one would guess that most carriers will continue to support GSM for at least 10 more years, if not longer. UMTS systems either use GSM SIM's, or, more commonly, a new type of SIM called a "USIM", which is backwards compatible with the GSM SIMs. You can see AT&T switching over the USIM's in the US since if you buy a 3G UMTS phone - it will come with one of the new SIMs.

Still, for what it's worth, both Verizon and Sprint have website-based systems for activating, and transferring phones, and they have a slick system for transferring contacts over their network. So it's not really that painful from what I have seen, to transfer contacts on and off of CDMA phones. And while we are at it, a several GSM phones - most notably the iPhone - don't allow transferring of contacts to and from SIM cards (although for the iPhone, there's a 3rd part app that enables it).

 

[Oyeve]

I had a real bottom of the barrel cingular phone that would spew so much interference that it would disconnect my PBX line if I got acall.