Book contents
- Frontmatter
- Contents
- Preface
- 1 Introduction
- 2 Impedance matching
- 3 Linear power amplifiers
- 4 Basic filters
- 5 Frequency converters
- 6 Amplitude and frequency modulation
- 7 Radio receivers
- 8 Suppressed-carrier AM and quadrature AM (QAM)
- 9 Class-C, D, and E Power RF amplifiers
- 10 Transmission lines
- 11 Oscillators
- 12 Phase lock loops and synthesizers
- 13 Coupled-resonator bandpass filters
- 14 Transformers and baluns
- 15 Hybrid couplers
- 16 Waveguide circuits
- 17 Small-signal RF amplifiers
- 18 Demodulators and detectors
- 19 Television systems
- 20 Antennas and radio wave propagation
- 21 Radar
- 22 Digital modulation techniques
- 23 Modulation, noise, and information
- 24 Amplifier and oscillator noise analysis
- 25 The GPS Navigation system
- 26 Radio and radar astronomy
- 27 Radio spectrometry
- 28 S-parameter circuit analysis
- 29 Power supplies
- 30 RF test equipment
- Index
6 - Amplitude and frequency modulation
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- Preface
- 1 Introduction
- 2 Impedance matching
- 3 Linear power amplifiers
- 4 Basic filters
- 5 Frequency converters
- 6 Amplitude and frequency modulation
- 7 Radio receivers
- 8 Suppressed-carrier AM and quadrature AM (QAM)
- 9 Class-C, D, and E Power RF amplifiers
- 10 Transmission lines
- 11 Oscillators
- 12 Phase lock loops and synthesizers
- 13 Coupled-resonator bandpass filters
- 14 Transformers and baluns
- 15 Hybrid couplers
- 16 Waveguide circuits
- 17 Small-signal RF amplifiers
- 18 Demodulators and detectors
- 19 Television systems
- 20 Antennas and radio wave propagation
- 21 Radar
- 22 Digital modulation techniques
- 23 Modulation, noise, and information
- 24 Amplifier and oscillator noise analysis
- 25 The GPS Navigation system
- 26 Radio and radar astronomy
- 27 Radio spectrometry
- 28 S-parameter circuit analysis
- 29 Power supplies
- 30 RF test equipment
- Index
Summary
Modulation means variation of the amplitude or the phase (or both) of an otherwise constant sinusoidal RF carrier wave in order that the signal carry information: digital data or analog waveforms such as audio or video. In this chapter we look at pure amplitude modulation (AM) and pure frequency modulation (FM). Historically, these were the first methods to be used for communications and broadcasting. While still used extensively, they are giving way to modulation schemes, mostly digital, some of which amount to simultaneous AM and FM.
The simplest form of AM is on/off keying. This binary digital AM (full on is a data “1” and full off is a data “0”) can be produced with a simple switch, originally a telegraph key in series with the power source or the antenna. The first voice transmissions used a carbon microphone as a variable resistor in series with the antenna to provide a continuous range of amplitudes. With AM, the frequency of the carrier wave is constant, so the zero crossings of the RF signal are equally spaced, just as they are for an unmodulated carrier. The simplest FM uses just two frequencies; the carrier has frequency f0 for data “zero” and f0 + Δf for data “one.” FM is usually generated by a VCO (voltage-controlled oscillator). For binary FSK (frequency shift keying), the control voltage has only two values: one produces f0 and the other produces f0 + Δf.
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- Information
- Radio-Frequency ElectronicsCircuits and Applications, pp. 54 - 66Publisher: Cambridge University PressPrint publication year: 2009
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