When my tv is on and i am textin or callin in close(<4 meters) proximity to tv, i hear this semi rythmic tone. i have a nokia 3120, if that counts. what is it, and have any other dopers experienced the same?
Thanks,
Jason
I had a Nokia 3650 and 8290(?) that did the same thing to my car stereo - not all the time, but every few miles (WAG - when leaving the signal from one cel phone tower and locking on to another?), enough to make driving in the car with the cel phone on very annoying.
This happened with two GSM phones but not with older TDMA phones, from AT&T Wireless, and was a primary motivator for switching cel phone companies for me. I have not experienced anything like it with phones from Virgin, Cingular, or Sprint.
well, i’m with cingular, and i think its the transmittin signal. the tv must me on for it to work, and you usually are calling or texting when it happens. it occasionally does it, just for the hell of it i guess.
Cell phones transmit and receive radio waves (that’s how they work). One of the first things they teach you in EE school is how simply a radio receiver is, and how easy it is to “accidentally” make one when you are making some other kind of circuit. All you need is an antenna, a tuner, and a decoder. The antenna can just be any bit of wire, or trace on a circuit board. A tuner is just a resonnant circuit, and circuit boards make natural resonnances just by the way they are built. For the decoder, all you need is something that conducts better in one direction than the other. Diodes and transistors both work quite well, but so do some other oddball things like a razor blade and a piece of pencil lead. Add in an amplifier, and you can take a really small radio signal that has been accidentally received by your equipment and turn it into a really large signal that you can hear. Televisions, computer speakers (especially the amplified kind), car stereos, CD players, etc. all can pick up signals from cell phones and other radio transmitters like a walkie talkie or even something like a neon sign.
A lot of people complain about their computer speakers “chirping” when a cell phone is placed nearby, due to the cell phone periodically staying in contact with the tower so that the phone system knows it’s there.
If by rhythmic you mean a kind of buzzing sound, what you are hearing is the radio/TV/whatever picking up the radio emissions of the cell phone (as mentioned above). The TV/radio/whatever isn’t tuned to the same frequency that the cell is transmitting on, but radio transmitters/receivers still transmit/recieve a little bit on the frequencies that they are not tuned to. Due to their close proximity, the relative signal strength is fairly large compared to the much-farther-away (but much stronger) TV/radio transmitter.
However, that isn’t the whole story. The main reason you can hear the buzzing (rather than a very faint bit of white noise) is that the cell in question is using a TDMA (Time-Domain Multiplexing) protocol. TDMA phones share channels simultaneously by dividing the channel into time-based chunks. Therefore, rather than transmitting continuously, the phone transmits in little bursts. It’s the “bursty” nature of the transmission that makes the distinctive buzz. The phone transmits whenever it’s making or receiving a call (of course), but also periodically just to say “hi, I’m here” to the network. You’ve probably noticed that the buzz starts a couple seconds before the phone rings, as the phone and cell network setup the call.
Analog or CDMA phones don’t exhibit this phenomenon, because they transmit continuously, and in the case of CDMA they transmit using spread-spectrum, meaning that the radio energy is spread out over a much wider frequency range and has less impact on a reciever tuned to a specific frequency.
I’ve seen (actually heard) this quite a lot; usually when a mobile phone is put close to a pair of cheap speakers like those used on many a desktop PC. It sounds sort of like dit-di-dit…dit-di-dit…dit-di-diiiit…
The reason it is picked up by the speakers is detailed by others above; essentially, it’s all too easy to make an audio circuit such as an amplifier that is also a radio receiver. The signal itself is just the phone communicating with the network, which it does periodically even if you aren’t making or receiving a call. It’s not uncommon for this sound to immediately precede an incoming call and for this reason, some people wonder how the phone ‘knows’ you were just about to get a call - it’s like this:
-A person dials your number
-They perceive a short delay (during which time the network is attempting to contact your handset)
-The caller hears the ringing tone on their phone, but your phone may still not actually be ringing
-The network and your handset finish their negotiations
-Your phone rings and you answer it.
In this case, the interference you hear on your speakers is your handset’s side of the ‘are you there?’ conversation that the system performs before connecting the call.
I always thought this was true. I have a Samsung/Cingular phone and I know exactly what we are talking about here. Happens with my TV and my Car Stereo, but not my PC … yet. I figured it was morse code for some reason. :smack: