Radio interference

[yachtie]

Can anyone please explain why mobile phones cause our radio to bleep randomly when neither of them is being used?

[boxtops]

It's texts going through, it happens to me too - if my phone is by my bedside radio instead of downstairs, my radio makes a bleeping racket every time our neighbours send texts.

[Buenchico]

Even if there are no texts, you will still experience interference on a radio (or, for example, a PA system, near to the phone).

Let's suppose that somebody calls you. If the mobile phone system didn't know where you where, it would be necessary for the call to be routed to every mobile phone transmitter in the world, so that the one which you happened to be closest to could connect with your phone. Given that millions of calls to mobile phones are being made at any one time, the system would be unable to cope.

So your incoming call is only sent to the transmitters closest to you. In order for that to happen your phone periodically sends out a signal, declaring "I am here" to the nearest phone transmitters. A transmitter then sends back a signal saying "Thanks. Information received".

In order to conserve battery power, the "I am here" signal is initially sent at very low power but, if no reply is received from a transmitter (because your phone is in a poor reception area) the "I am here message" is repeated at increasingly higher power until an acknowledgement is received.

It's those "I am here" signals which your radio is picking up.

Chris

[yachtie]

Thanks for your help

[ChuckFickens]

Methyl obviously thinks that if you turn your phone off for a couple of days every single mobile phone mast in the world is sending out a signal asking if your phone is alive.

[ChuckFickens]

You really believe that would be a sensible way to set up a network?

Every single mobile cell tower permanently broadcasts a system identification code on a reserved carrier channel, when you turn on a phone it firstly listens for a SID, if it hears a SID broadcast and the phone recognises it the phone then sends a registration request to the MTSO of the network the SID is being broadcast from, it's this registration request that can be heard on a radio close to the phone.

In simple terms, the SID tells the phone it's worth checking in, the phone initiates the check in.

[Old_Geezer]

The radio is just picking up the messages sent as interference.

The mobile is just ensuring the network knows where it is. If the network loses track of your mobile it won't know where to send incoming calls and your caller will be told your mobile is unobtainable.

[Old_Geezer]

"It is true that the phone initiates the check in."

Clearly. The network isn't going to be sending out billions of "are you there" signals all the time in the hope that something will respond. It is up to the mobile to indicate it is in the vicinity and would like to connect.