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¡). Other components more specific to FM receivers are mixers combined with local oscillators used for frequency manipulation, limiters to control amplitude, de-emphasis and other filter circuits.
2
Mathematics of FM
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¡). Other components more specific to FM receivers are mixers combined with local oscillators used for frequency manipulation, limiters to control amplitude, de-emphasis and other filter circuits.
2
Mathematics of FM