Fm Receivers
Abstract
This paper will discuss the design of an FM receiver. It will begin with a brief historical
backdrop of FM broadcasting and its use in society. It will continue by providing the
necessary mathematical background of the modulation process. Furthermore, it will
enumerate some of the advantages of FM over other forms of modulation, namely AM.
Finally, the paper will discuss the design of a basic FM receiver as well as introduce
some circuits and circuit components which the reader may not be familiar with.
Introduction
Frequency modulation (FM) was invented in 1936 by an American electrical engineer/
inventor named Edwin H. Armstrong. Possessing numerous advantages over the existing
AM broadcasting system, as will be discussed later, in combination with relatively low
cost of implementation, resulted in its rapid growth. In the years following World War
Two, there were 600 licensed stations broadcasting in the U.S. By 1980, the number grew
to 4000. On another historical note, in 1961 stations began broadcasting in stereo.
The basic receiver design consists of the following components. An antenna is used to
convert electro-magnetic waves into electrical oscillations. Amplifiers are used
throughout the receiver to boost signal power at radio, baseband and intermediate
frequencies. The core of the FM receiver, the discriminator, comes in various circuit
forms and is used in detection and demodulation. Basically, its role is to extract the
intelligence or message from the carrier wave. Another component, essential in most
electronic circuits, is the power supply (DC or AC converted to DC). Finally, a
transducer (speaker in the case of Radio) is needed to convert the message signal into its
final form (audio, mechanical, etc¡Â). Other components more specific to FM receivers
are mixers combined with...
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