The control unit contains handset with speaker and microphone. It also contains a complete touch tone dialing circuit.

It is operated by a separate microprocessor drives the LCD display and other indicator .It also implements all manual control functions .

The microprocessor memory permits storage of often called numbers and an auto dial features .

The demodulated signal coming from the receiver is amplified by an audio amplifier and applied to the loudspeaker whereas the electrical equivalent of voice signal is produced by the microphone & amplified by the audio amplifier.

This signal acts as the modulating signal and applied to the modulator.