ample, Antennas are also known as aerials. Basic features of radio communication systems CHAPTER 2. 1 Volts Volts Fig. 2.1-2 A sinusoidal radio carrier wave. we can type, use a pencil, ultraviolet ink, etc. However, Volts the reader must be able to decipher (demodulate) the information provided. For example, if we use ultraviolet ink, the reader must also use ultraviolet light to decipher (demodulate) the message. Hence the modulation and demodulation methods must also be compatible. In the discussions that follow we are only discussing modulation and demodulation methods; not the modu- lation information. We also tend to use sinusoidal waves for our explanation. This is because a great mathemati- cian, Joseph Fourier, 4 has shown that periodic waveforms Volts of any shape consist of one or more d.c. levels, sine waves and cosine waves. This is similar to the case in the English language, where we have thousands of words but, when analysed, all come from the 26 letters of the alphabet. Hence, the sinusoidal wave is a useful tool for un- derstanding modulation methods. We now return to our simple radio carrier wave which Fig. 2.1-3 Amplitude modulation waveforms: (a) modulating is the sinusoidal wave 5 shown in Figure 2.1-2. wave; (b) carrier wave; (c) modulated wave. A sinusoidal wave can be described by the expression its frequency (wc) according to our information - this is called frequency modulation and will be described Vc = Vc cos (wct++c) (2.1.1) in Section 2.1.3.2; where its phase (c) according to our information - this is known as phase modulation and will be described Vc = instantaneous carrier amplitude (volts) in Section 2.1.3.3; Vc = carrier amplitude (peak volts) or we can use a combination of one or more of the Wc = angular frequency in radians and Wc = 2nf where methods described above - this method is favoured fc = cartier frequency (hertz) by digital modulation. Oc = carrier phase delay (radians) If you look at Figure 2.1-2, you can see that a sinu- 2.1.3.1 Amplitude modulation soidal wave on it