ompanies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Radio Engineering Concepts Key Radio Concepts Electric Field Magnetic Field Wave Motion Figure 1.1 An electromagnetic radio wave. the letters to form words. In this case, the formatted message is a sequence of letters, a digital signal. The meaningful message in telephony is primarily spoken voice. The formatting stage is done with a microphone and amplifiers to form an electrical voltage over time that represents the speech, an analog signal in this case. If this signal is fed into an amplifier and a speaker, then we hear meaningful voice output. 1.2 Frequency In addition to their magnitude, analog signals such as audio, electricity, and radio also have the attribute of frequency. We all know frequency as the pitch of a sound or the station numbers on a car radio, but frequency is a deep, basic, fundamental, primal mathematical concept that deserves some attention. The simplest view of frequency is that it is the number of waves that pass a given point at a given time. In this simplified view, wavelength is in inverse ratio to fre- quency, with the speed of transmission as the constant. We measure frequency in cycles per second, or hertz (Hz). 1 Frequencies we use in real life vary considerably. We have the very low 50 or 60 Hz of electrical power from the wall outlet. Sound we hear is air pressure waves varying from 20 Hz to 20 kHz.2 Our AM radio stations operate from 500 kHz to 1.6 MHz, and FM and older broadcast More mathematical texts often measure frequencies in radians per second and usually use the Greek letter omega w for radian frequency values, where W = 2nf. 2While almost everybody reading this knows that kHz stands for kilohertz, 1000 hertz, some of the other prefixes may be more obscure. The entire list is in the "Physical Units" section at the end of this book. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All righ