BibTeX
@MISC{_1broadcasting,
author = {},
title = {1 Broadcasting Systems Broadcast (Radio, TV) Networks},
year = {}
}
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Abstract
In its most common form, radio is used for the transmission of sounds (voice and music) and pictures (television). The sounds and images are converted into electrical signals by a microphone (sounds) or video camera (images), amplified, and used to modulate a carrier wave that has been generated by an oscillator circuit in a transmitter. The modulated carrier is also amplified, then applied to an antenna that converts the electrical signals to electromagnetic waves for radiation into space. Such waves radiate at the speed of light and are transmitted not only by line of sight but also by deflection from the ionosphere. Receiving antennas intercept part of this radiation, change it backto the form of electrical signals, and feed it to a receiver. The most efficient and most common circuit for radiofrequency selection and amplification used in radio receivers is the superheterodyne. In that system, incoming signals are mixed with a signal from a local oscillator to produce intermediate frequencies (IF) that are equal to the arithmetical sum and difference of the incoming and local frequencies. One of those frequencies is applied to an amplifier. Because the IF amplifier operates at a single frequency, namely the intermediate frequency, it can be built for optimum selectivity and gain. The tuning control on a radio receiver adjusts the local oscillator frequency. If the incoming signals are above the threshold of sensitivity of the receiver and if the receiver is tuned to the frequency of the signal, it will amplify
Keyphrases
electrical signal system broadcast radio receiver intermediate frequency local frequency electromagnetic wave local oscillator frequency single frequency oscillator circuit arithmetical sum common form carrier wave antenna intercept part incoming signal common circuit local oscillator video camera radiofrequency selection optimum selectivity
