We're sitting in the right place to start, since this time we'll follow the juice back from the microphone that's connected to that black cord we see running over the circuit board. That's the relay . The relay is a kind of switch which connects either the transmit or the receive circuits together. It's controlled by the push button on the microphone. That's how the parts common to both transmit and receive are switched back and forth from one to the other.
Cellular telephones use a voice activated transmitter which automatically trips the relay.
A cellular phone uses one frequency to transmit on and another one to receive on. This lets both callers talk in a normal, back and forth fashion, just like a regular land line telephone. Since walkie talkies use a single frequency to both talk on and listen, each party must wait their turn to transmit. A voice activated microphone would not work well since you might start transmitting when the other party is speaking, consequently, you would not be heard. Let's take a gander at our tour map so we all know where we're going.