Comment That's the way that GSM phines operate (Score 1) 110
Because that's the way that GSM phones operate.
In order to achieve Full Duplex operation, it receives for half the time, then transmissions for half the time.
These transmit data bursts result in a deeply Amplitude modulated RF envelope.
This is why you hear Brrrp, Brrrp when you put your GSM phone near a pair of cheap loudspeakers.