Why do cell phone ringtones play through television speakers?

[thomasxc]

ive noticed several times that when I am watching tv, and my phone rings, that my ringtone will actually play through my tv speakers. does anyone know why that happens?? thanks.

 

[GetPhysical]

I think its just your hearing. Unless you have some super computer nerd friend who somehow rigged your phone top play through the TV.

 

[thomasxc]

i highly doubt that its just my hearing, and this is why. it will happen when I am with other people, and they will hear it as well.thats how i first found out about it... a week ago in class, we were watching tv and we could tell every time someone sent a text message because it made a very specific, unique noise. we even tested it out to make sure it wasnt anything else..

 

[f95toli]

That speakers make a NOISE is not at all unusual. Your phone sends out a relatively powerful signal back to the transmitting tower when they initiate the connection (usually a number of "pulses", this usually happens a few seconds BEFORE the phone actually rings).
Now, this just a radio signal so if it picked up and then passed through some non-linear component (e.g. a protection diode in the speaker) the result will be a low-frequency signal which in turn can be played back by the speaker. The principle is exactly the same as for an old crystal radio.

However, this would NOT explain why the TV plays the ringtone; what I describe above will sound more like a "Morse" signal (a few short beeps with some noise) and it not a pleasant sound; so unless you have a very strange taste in ringtones it will not sound like your phone.

 

[Lambduh]

This also happens to me. A few seconds before my phone rings i'll get an audible hiss from my stereo if my phone is near enough to it. I can only assume that the cell phone is inducing noise in the stereo. It must be from the cell phone and not from the tower as it doesn't happen unless the cell phone is receiving a call. Otherwise the noise would be constant as the cell towers are always transmitting/receiving data. That makes sense to me as the power from the cell phone will be much higher than the power from the cell tower (unless you're standing up on top of it) :)

 

[Danger]

Keeping in mind that I'm a totally inept follower of technology... are these phones BlueTooth enabled? Just wondering if they're searching for companionship.

 

[rcgldr]

There's a big gain jump in the audio power amp of your TV. My guess is that the preamp elements pick up the noise through antenna effect and the audio power amp boost this enough to be audible. A cell phone in my wife's car can cause the speakers to click when the radio is off, but this never happens in my car or if at home with the cell phone near the stereo. I'm guessing that somehow the power amp portion in my wifes car must be stuck on.

If a cell phone is close to my computer it will create video noise on my monitor, it appears to interfere with the logic in the graphic card or monitor, as I assume there isn't a significant magnetic field at work here.

 

[Borg]

I used to have a car alarm that transmitted a signal over FM frequencies a few seconds before the main alarm when it went off. It was a very strong signal and made nearby radios sound like they were about to explode. I loved setting it off at traffic lights when someone would pull up with their stereo blasting everyone. It never failed to get them to turn down their stereo! Your cell phone apparently is sending out signals that your TV can hear. Have you tried it around other televisions?

 

[f95toli]

Keeping in mind that I'm a totally inept follower of technology... are these phones BlueTooth enabled? Just wondering if they're searching for companionship.

No, Bluetooth shouldn't cause this type of effect, it is a short-range low-power standard.

The main reason why the "beeps" are so strong is that the cell phone initially transmits at maximum power (which can be significant for a cell phone); once it has "negotiated" with the tower it will reduce the power in order to conserve energy.

This does not mean that the effect disappears completely (there is a good reason why you are not allowed to use cell phones around sensitive electronic equipment); interference from cell phones can be quite a problem for me when I am doing measurements in the lab (we do have a "No mobile phones allowed" sign, but many people forget to turn their phone off)

Whether or not you hear the "beeps" will depend on many factors: the type of phone, the strenght of the non-linearity that down-mixes the signal, what is acting as an antenna (a short piece of cable, a trace on the PCB etc ), the gain in the pre-amps etc

This phenomena was very common with older GSM phones; it doesn't seem to happen quite as often with 3G.

 

[thomasxc]

well, f94toli, i could have swore that it was playing the actual ringtone through the tv. is it at all possible that the tv could somehow make the phone louder?? but i have gotten the "morse" signal as well, and generally just for text messages. and I am not sure about the bluetooth part. mine isn't enabled.

 

[rcgldr]

well, f94toli, i could have swore that it was playing the actual ringtone through the tv.

This can happen via the antenna effect as I mentioned before, the audio frequency electrical wave pattern for the ring tone going to the cell phone speaker gets picked up through antenna effect in the pre-amp stage of the TV receiver and then gets amplified by the power amp. You could try selecting a disabled input (so no other audio) on the TV and turning up the volume to confirm this.

In the olden days, by cycling bits on and off in mini-computer registers at audio frequences, "music" could be heard via an AM radio placed close to the mini-computer. At one job, there was a high speed optical paper tape reader (600 frames per second) that used a fast moving small cylinder to act as a brake and I could generate tones with it by placing a few layers of paper tape under it but not reaching the pinch rollers that moved the tape. To impress co-workers, I'd play music with the tape brake, but have a "dummy" AM radio near the cpu so the co-workers thought it was the typical radio thing until I then took the radio and walked away with it, leaving the music playing. It was fun watching them trying to figure out where the sound was coming from. I was told by the company that made the reader, that the tape brake could take this as the relatively high frequency combined with the several layers of paper tape reduced the g-forces and current compared to normal operation.

 

[thomasxc]

haha.cool.