Real-time communication system

A real-time communication system transfers information from an input to an output as it is produced. It does not deliberately delay sending or reproducing the information, although transmission and processing can take a short time.

The information passes through a chain of stages. For a sound signal transmitted by radio, the chain works as follows:

1. Input transducer: A microphone converts sound into an electrical signal that carries the information.
2. Modulator: The information signal is used to vary a carrier signal, producing a modulated signal that can be transmitted.
3. Amplifier: The modulated signal is strengthened before transmission.
4. Transmitter: A transmitting aerial sends the signal out as radio waves.
5. Transmission path: The radio waves carry the signal from the transmitter to the receiver.
6. Receiver: A receiving aerial detects the radio waves and converts them into an electrical signal.
7. Second amplifier: The received electrical signal is strengthened.
8. Demodulator: The information signal is recovered from the modulated carrier.
9. Output transducer: A loudspeaker converts the recovered electrical signal into sound.

The input and output transducers therefore convert information between electrical signals and forms that can be produced or detected outside the system.