Ch 8Modulation and Demodulation — 2nd PUC Electronics, concept-first.

Every wireless message you receive — a radio broadcast, a mobile call, a television signal — begins as a low-frequency information signal that, on its own, simply cannot travel far or be radiated effi…

The purpose of any communication system is to carry information — a message signal — from a source to a distant receiver.

Amplitude modulation (AM) is a modulation process in which the amplitude of a high-frequency carrier wave is varied in accordance with the instantaneous value of the modulating signal, while the frequ…

To describe an AM wave mathematically, let the modulating signal be

The signal-to-noise ratio at a receiver depends on the received signal power, which must be much larger than the noise power.

In practice a carrier is rarely modulated by a single pure tone. A real information signal — speech, music, video — contains many frequencies at once, so the carrier is modulated simultaneously by sev…

Frequency modulation (FM) is a modulation system developed in 1936 as an alternative to AM. Amplitude modulation is not an efficient way to transmit voice and music, and it is vulnerable to noise.

Demodulation, also called detection, is the process of recovering the original modulating (baseband) signal from a modulated carrier wave.

A radio receiver is the equipment that picks up the modulated radio wave from the antenna and turns it back into sound.

A transmission line is a system of conductors that carries electrical energy — as guided electrical waves — from one point to another, for example linking a transmitter or receiver to its antenna.

An antenna is a device that radiates electromagnetic waves into space (when transmitting) and captures them (when receiving).

In digital communication, information is encoded as discrete (digital) signals — sequences of 1s and 0s — and transferred electronically to the recipient.

This chapter completes the study of how a transmitted message is recovered and reproduced, and how the signal is guided and radiated.