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How to Avoid Mobile Phone Interference w/ Speakers
EnzoTen asks: "Everyone has been sitting at their desk rockin, jamming, or groovin to their favorite tunes. You are in a trance, getting work done... then... BZZZPT... BZZTP..BTT.. BZZZZZZZZPTT... the blood curdling noise of your cell phone interferes with your desktop speakers playing 4 times the volume of your music and it takes everything in you not to flip your desk upside down, or throw your mobile phone across the room. Is there anyway to avoid mobile phones interfering with speakers? Are there speakers available that are shielded from this type of interference?"
it happens to me with my ATT/Cingular GSM phones and affects both of my car stereo systems and my desktop speakers, but not my hifi/amp setup. It's not as annoying as the submitter describes, but it's a very audible, very noticeable series of clicks and burps. Lasts about three seconds, every ten, fifteen minutes. I assume it's interference from some kind of GSM syncrohnisation signal, but I'm not an EE. :)
-EvilMagnus
This problem affects GSM phones much more than CDMA phones. GSM uses a time-division scheme, where the phones transmit in 570ns bursts, at a rate of around 217 bursts/sec.
I have the same experience. It really is very, very annoying.
One of the RF techs at my company apparently modified his computer speakers to filter out the noise. I'd like to find out exactly what it was that he did.
The solution is to properly shield the speakers and speaker wire. The speaker wire behaves like an antenna, coupling the signal into the audio amplifier, where it is detected and amplified. It's behaving like a crystal radio, a primitive type of AM radio receiver.
Mea navis aericumbens anguillis abundat
i'm frankly a bit surprised that so many people don't know what you're talking about - i know it very well, and it even affects my monitors.i actually like it -you get to see how long the cell-tower to phone negotiating takes, since it starts happening a couple of seconds before the phone actually rings or receives a SMS.
the solution, i guess, is simply to use more expensive shielded speakers, since that's what faraday cages do.
I moved my phone about 17 inches to the right. Worked fine.
Seriously, just move the speakers and phone placement until they don't interfere with each other. A couple decades ago every bit of electronics you bought came with a piece of paper that told you to do this if you got radio or television interference. I always thought it was silly, but maybe that slip of paper needs to go back into boxes.
--
Evan
"$30 for the One True Ring. $10 each additional ring!" -- JRR "Bob" Tolkien
There are two places you can solve this problem:
#1, get a better cell phone. With TDMA phones (GSM, D-AMPS, iDEN) you get a lot of noise as the transceiver switches on and off several times a second, transmitting at full power. iDEN phones (NexTel) have always been *by far* the worst about this, in my experience. If you get a CDMA phone (eg, Verizon), the phones on a cell share a common, continuous, low-level signal, which does not cause this kind of interference.
#2, shield your amplifier. (In cheap computer speakers, it's built into one of the speakers, or the subwoofer.) Surround it in tin foil, and ground the foil. Other possibilities are poor grounding on the signal wire - replace it with a shielded wire, and ground the shield to your computer's case and where it reaches the amp.
90% of the time it happens just before I get a call/text, so I quite like the early warning.
Come as you are, do what you must, be who you will.
Symptom: When you use X, Y doesn't work properly.
Cause: Due to a design deficiency in X, Y sucks when used in conjunction with X.
Solutions:
- Don't use X
- Don't use Y
- Render yourself unable to notice the problem
Keywords: omg bzzt bzzzzzWhat the hell is my phone transmitting when i'm not receiving a call?
It's periodically sending your GPS location to the government who's building a huge database of people's movements, to correlate against all sorts of crimes ranging from terrorist attacks and murders to petty theft and jaywalking.
The RIAA has shown interest in this as well. They want access to the data so they can draw up a list of people who walked by a record store without stepping inside and buying a CD. They claim it's not only in their own interest, but for national security as well, since anyone found guilty of such a crime is a threat to the national economy, and therefore a terrorist. But don't worry, the government is protecting you and is fiercely negotiating with the RIAA on your behalf. They finally realised what a bunch of nutcases these RIAA folk really are, they're sick of being pushed around by some corporate lobbyists, and are now actively pushing for a rewrite of that RIAA bill that would change the wording from "terrorism" to a mere "theft". And it looks like they might even have a chance of winning this one...
OK, and now for the serious answer: a cellphone tower can only support a limited number of simultaneously connected cellphones. It therefore needs to know exactly when a cellphone leaves its range, or disconnects from the network altogether, so it can free up its connection slot for use by another cellphone. Normally a phone communicates a disconnect to the tower whenever possible (for example if it's getting out of reach and connects to another tower, it then disconnects from the first and the connection gets transferred gracefully from the old tower to the new one, even in the middle of a conversation). However, if you just yank out the batteries, the phone gets utterly destroyed, you suddenly enter a cage of faraday or even an underground tunnel, ... the phone will have no time to notify the tower, so the tower needs to check up on supposedly connected phones from time to time to check that none of them are MIA. It's basically similar to an ICMP ping on the Internet. And that's what you hear over your speakers. Similar thing happens right before a call or SMS comes in, or when you dial out: there's two-way communication, and the RF interference the cellphone puts out is picked up by your audio equipment.
Install windows on my workstation? You crazy? Got any idea how much I paid for the damn thing?
GSM is a TDMA (Time Division Multiple Access) system. This means a single physical channel is divided up in time for multiple people to share. A single physical channel is just a frequency range, such as 890-890.2 MHz. Each physical channel is divided up in time into what are called timeslots. Timeslots are grouped by 8's into what are called frames. Each timeslot lasts 0.577ms, and a frame is 4.615ms. When your phone is communicating with the base it is assigned a single timeslot in each frame. This means it is transmitting ON off off off off off off off ON off off... and the ON's are spaced 4.615ms apart (the frame duration). 1/4.615ms gives you 216.7Hz, which means that if (when?) it is picked up by other electronics, it is most definitely in the audio band and you will hear it. The RF transmissions die off very rapidly with distance from the antenna, which is why moving the phone a small distance away is sufficient. What else... when you hear the interference before receiving a call/SMS, this is what is happening 1) one or more base stations broadcast "hey you" to the geographic region where your phone is (your phone is always listening for this) 2) your phone contacts a specific base station requesting a channel (AUDIBLE) 3) the base station responds, assigning a channel 4) your phone goes to that channel, authenticates, etc. (AUDIBLE) 5) phone finally rings / SMS is sent
Slashdot comments at its best. Useless.
If you do not recognize the problem, it just might be that you
a) do not experience it -> cannot help.
b) do not hear it -> cannot help.
c) notice it, but do not want to help!
In every case, it might have been a good idea to wait and see if more
intelligent and/or helpful people chime in, and might provide an answer to
the riddle. And until that time, just shut up. You probably will just look
foolish if you try otherwise .
I actually *understand* the physics behind that phenomenon, and alas, there
is no better solution than what was provided in another response: put your
cell phone at least one foot away from the speakers. The problem is Maxwell:
in order to send a signal successfully to the next station (remember: this
is most likely indoors, as speakers are less usefull outside, and thus, there
is probably a wall, which has to be penetrated by electromagnetic waves) the
cell phone has to "pump up the volume".
The energy is degrading with the second power of the distance to the cell
phone, so: putting it at double distance to the speaker (or the next
station, for that matter) will lower the received energy by 75%. Same is true
for the station, but that is farther away to begin with.
educating people every day,
Dscho
As an audio applications engineer for a large semiconductor company -- this is the single biggest compaint we have from customers using CMOS IC amplifiers. You will get it from almost any audio system that's near a cell phone (or 802.11b RF transmitter -- they have 50Hz packet rates that are audible from the 2.4GHz baseband signal).
What ususlaly catches it is the speaker wires -- they act like giant antennas. 900MHz and up takes only a few centimeters to make a decent antenna, so long speaker cables are a prime target. The high frequncy (which you can't hear) couples on the output lines (typically) and goes back through the gain setting resistors on the amp to rech the amplifier input, where the packet rate (not the 2.4GHz to 900MHz baseband) is rectified and amplified. What you hear is the resulting buzz.
Your cell phone itself doesn't shield this -- then it wouldn't work! The best thing to do is to shield your speakers, wire, and audio system it may be near. A faraday cage (as described by others here) will work great. Plastic-metallic shielding (like that used in anti-static IC or computer part bags) also works wonders.