Q.Explain the necessity of a carrier wave in communication.

[!TLDR] A carrier wave is needed because a raw low-frequency signal cannot be transmitted efficiently (impractical antenna, inefficient radiation) or separated from other stations without it. [!ANSWER] Without a carrier wave, a low-frequency signal c …

Sections 13.5.2 and 13.6 together lay out the necessity of a carrier wave. First, an efficient transmitting or receiving antenna needs a length of at least about $\lambda/4$; a raw audio signal (say, 15 kHz) would need an antenna roughly 5 km long, which is completely impractical. Second, even setting antenna size aside, low-frequency waves are radiated far less efficiently than high-frequency ones for a given antenna, so power would largely be wasted. Third, if multiple transmitters sent their signals directly without distinct carriers, the signals would mix together and become impossible for a receiver to separate. A high-frequency carrier wave -- with the low-frequency signal impressed onto it by modulation -- solves all three problems at once: it needs …

Combine the antenna-length, radiation-efficiency, and station-separation reasons from sections 13.5.2 and 13.6 into a si …

Giving only a single reason (most commonly just the antenna-length issue) when a fuller explanation co …