Q.Explain briefly why the practical size of a transmitting antenna and the power that antenna can efficiently radiate together make it impossible to transmit an audio-frequency signal directly, without first shifting it onto a much higher carrier frequency.
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Start your 14-day free trial to unlock the full solution →Antenna size. Efficient radiation from an antenna needs its physical length to be comparable to (typically a significant fraction of) the wavelength of the wave being radiated. Audio frequencies (a few kHz) correspond to wavelengths of many tens of kilometres -- no antenna of that size can be built or erected.
Radiated power. Even setting size aside, for an antenna of fixed, practical length, the power it can radiate efficiently increases sharply as the driving frequency rises (for a short antenna, roughly as the square of length/wavelength); at audio frequencies this ratio is tiny, so almost none of the electrical power fed to a practical-sized antenna would actually leave it as radiation -- it woul …
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