I saw a demonstration of an RF detector being brought close to a mobile phone. As the detector was moved away, the number on it dropped to zero. How can that be? Shouldn’t there be some RF signal from the phone all the way to the cell tower, so that the phone can communicate with the tower?

Question

I saw a demonstration of an RF detector being brought close to a mobile phone. As the detector was moved away, the number on it dropped to zero. How can that be? Shouldn’t there be some RF signal from the phone all the way to the cell tower, so that the phone can communicate with the tower?

In: Technology

Answer 1

A mobile phone doesn’t constantly transmit at the highest power available. It is mostly inert to save battery life and is only listening to transmission from the tower (which the detector would count as part of the “ambient” RF field and not show, like the tare function on a scale). It gets a lot livelier when it is trying to use its radio to transmit. In the receive-only state the RF detector probably only detects the small interference caused by the phone’s internal power system and the processor/other digital stuff.