Why Handphone Signal Audiable in Speaker? - Page 1
Forum section: electronics / beginners

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 04, 2011, 04:15:24 pm
content: i usually put my handphone near my PC. when somebody call or send sms, i knew it before the hp ring because i can hear it in speaker. tet det tet 3-5 times for sms, indefinitely for a call, annoying! why? is it the GSM et al signal consist of audio frequency? dont tell me the fix, i know, put the hp away.

author: jahonen
author_rank: Super Contributor
timestamp: December 04, 2011, 04:18:44 pm
content: Audio circuits are not adequately shielded and modulated (think it as AM) RF-carrier will get demodulated. Thus you hear the modulation (transmit bursts) at audio frequencies.Regards,Janne

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 04, 2011, 04:24:18 pm
content: should i wrap my soundcard with tin foil to fix it? without putting my hp away?

author: Chet T16
author_rank: Frequent Contributor
timestamp: December 04, 2011, 04:24:44 pm
content: I used to have a wireless keyboard and mouse that was affected by a call or text coming in "it wold et annying by missig rndom leters"

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 04, 2011, 04:30:20 pm
content: it doesnt affect my wireless kb/mouse though, thats good. not sure but maybe its 2.4GHz wireless, or bluetooth.

author: baljemmett
author_rank: Unknown
timestamp: December 04, 2011, 04:57:02 pm
content: Quote from: Mechatrommer on December 04, 2011, 04:15:24 pmA little-known Australian video bloggercovered this subjecta couple of years ago. (Back in the days when he still had to do some really severe editing to fit within YouTube's 10-minute limit!)

author: don.r
author_rank: Frequent Contributor
timestamp: December 04, 2011, 05:15:40 pm
content: Happens all the time with land-line telephones and mobiles phones. I have a vacuum tube headphone amp that picks up my wifi signals. I built a Faraday cage around the tubes and its all good now. Generally, you want to find a solution in the receiver rather than the transmitter. Are the headphones wireless? If so, you may need to get a pair that use a different technology.

author: IanB
author_rank: Super Contributor
timestamp: December 04, 2011, 05:28:07 pm
content: Quote from: Mechatrommer on December 04, 2011, 04:15:24 pmIt's the well known GSM chirp. Switch to a new smartphone with 3G and it won't happen.

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 04, 2011, 07:07:25 pm
content: Quote from: baljemmett on December 04, 2011, 04:57:02 pm47MB? i like it! not like the current 200++MB files@don: my speaker is wired, i guess the signal is picked up from inside the PC, but the casing is metal, front is plastic, so i guess not enough as faraday cage. or maybe picked up by speaker's circuit/amp?@IanB: believe me, 3G is not so common here yet, or at least to me.

author: slateraptor
author_rank: Frequent Contributor
timestamp: December 04, 2011, 07:30:54 pm
content: Quote from: Mechatrommer on December 04, 2011, 07:07:25 pmI would have never guessed that the Tiger Cub economy of Malaysia was technologically lagging...or do you live in a rural part of the country?

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 04, 2011, 07:49:16 pm
content: i live in rural part where cochroaches and spiders are commoni think there 3G coverage now, or at least unstable or few 100s km away from me. i will try to figure this up when searching for 3G capable phone. i never like the newer design

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 04, 2011, 07:52:36 pm
content: ok watched dave's #23, now i know. i missed that vidz.

author: slateraptor
author_rank: Frequent Contributor
timestamp: December 04, 2011, 08:01:27 pm
content: Quote from: Mechatrommer on December 04, 2011, 07:49:16 pmGoes to show how spoiled us Americans are: I was disappointed when Google didn't select my city as a testbed for their gigabit network.

author: don.r
author_rank: Frequent Contributor
timestamp: December 04, 2011, 09:01:14 pm
content: Quote from: Mechatrommer on December 04, 2011, 07:07:25 pmYou would have to pinpoint the source of the interference. If its coming from inside the PC, then further shielding of the card may be required. Sometimes, audio cards come covered in metal shielding cans for just this reason. Otherwise, it could be inadequate shielding in your headphone cable or a poorly designed RF rejection circuit on the card. On small devices like iPods and such, the shielding is often used as an antenna to pickup FM radio so that shows you that proper RF bypass is needed on the cards output jack.

author: IanB
author_rank: Super Contributor
timestamp: December 04, 2011, 09:44:28 pm
content: Quote from: don.r on December 04, 2011, 09:01:14 pmThe GSM interference gets into almost anything with an audio circuit, and most things that don't. It's like a powerful jamming signal and very difficult to block. It is the main reason cell phones used to be prohibited in hospitals. What a phone was able to do to Dave's multimeter it is also able to do to medical devices.

author: don.r
author_rank: Frequent Contributor
timestamp: December 04, 2011, 11:18:24 pm
content: Quote from: IanB on December 04, 2011, 09:44:28 pmI feel this is more down to inadequate shielding and design of the hospital equipment. My GSM phone has no effect whatsoever on any of my audio or computer equipment although I can hear it when I use my cordless land line phone. At any rate, in this instance the OP may be better off finding a different phone technology if its a big issue. I would always treat the problem as one of shielding, however, to prevent any future issue or consider it a handy way of knowing when a call or text is coming in when you have your headphones on.

author: PeterG
author_rank: Frequent Contributor
timestamp: December 04, 2011, 11:52:14 pm
content: Most PCs have a metal chassis that acts as a fairly good RF shield. I would guess the sound is coming from the speakers internal amp. The amp used in many powered PC speakers is not well shielded causing this interference.Turning the phone on/off while next to the powered speaker will confirm.Just my 2 cents.Regards

author: ciccio
author_rank: Frequent Contributor
timestamp: December 05, 2011, 02:07:04 pm
content: GSM phones are powerful interference generators, more than other, even more powerful, radio transmitters.Their "galloping" interference is injected into any audio circuit.It is standard practice to demand to people listening to rock concert to switch off their phones, and I know that in many venues some (obviously illegal) "cellular phone jammers" have been installed to protect the audio quality.I design and install audio systems for a living, and this problem plagues me.Screening and shielding is, most of the times, of no help.Even transformer balancing, ground insulation, and other standard practices are. most of the times, of no help.Sometimes I question myself: I me, and not the big corporation manufacturing phones, was in the process of testing a GSM phone for CE compliance, will I get an approval?

author: jahonen
author_rank: Super Contributor
timestamp: December 05, 2011, 06:50:37 pm
content: I think that problem is that audio amplifiers are not built like a RF device. Simple "aluminium foil" shielding just is not good enough, there must be not any slots anywhere and all signals must be filtered at shield so that RF attenuates properly. Even most audio connectors are not good enough in shielding perspective. Most audio designers put their head in the sand if one tries to explain what is only effective grounding method in RF (heavy multipoint).Surprisingly, the audio parts of a mobile phone seem not to be disturbed greatly from nearby modulated RFso it is possible to do. But doing that would increase the cost so much that it is easier to leave it as is.Regards,Janne

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 07, 2011, 08:12:35 pm
content: Switch to a good quality digital amplifier. A digital signal has a high immunity to interference (very high for optical) and the amplifier itself would be well shielded to keep the harmonics of the carrier from escaping.At one point, it was common practice to perform a quick EMI susceptibility test using a cell phone. A surprisingly large percentage of modern phones are designed to eliminate that very problem, so that is not always a good test.

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 07, 2011, 11:25:45 pm
content: Quote from: NiHaoMike on December 07, 2011, 08:12:35 pmany suggestion in $100-200 range of PC speaker system?

author: deephaven
author_rank: Frequent Contributor
timestamp: December 08, 2011, 01:15:05 pm
content: Radio frequency interference is often picked up in the speaker wiring and possibly the ausdo input wiring. Try putting your phone near the wiring and see if the interference gets worse. If it is being picked up by the cable you might be able to filter it by passing the cable through a ferrite ring (preferably using several turns around the ferrite).