 standard metric for measuring the variability of a signal with respect to time. For example, the signal represented in Figure 3.9 is said to have a Broadband Telecommunications Technologies and Management 2G, 3G, 4G Allocated spectrum Frequency Wavelength Figure 3.8 Frequency of electromagnetic waves Time (s) Figure 3.9 A waveform with a frequency of 5 Hz frequency of 5 Hz. The maximum amplitude of the sine waveform here is 1 volt (V), named in honour of Alessandro Volta (1745-1827), the inventor of the battery. Similarly Figure 3.10 shows three waveforms (a, b and c) with frequencies of 5, 15 and 25 Hz, with maximum amplitudes of 1, 0.33 and 0.2 V. Figure 3.10 also shows the sum of these signals in (d), a waveform which has nearly a square wave shape. As Figure 3.10(d) is the sum of the three signals a, b and c, it has exactly three frequency components, 5, 15 and 25 Hz. The signal bandwidth is defined to be the maximum frequency component minus the minimum frequency component. Therefore, the signal of Figure 3.10(d) has a bandwidth of 20 Hz. Most natural signals contain many frequency components. An example is the human voice. Our voice is generated by vocal cords which resonate at a particular frequency which is then modulated into a range of frequencies and harmonics by our throat, mouth, teeth and lips. The range of human voice frequencies, as shown in Figure 3.7, is generally measured to be 300-3400 Hz. This means that the human voice frequency bandwidth is 3100 Hz. Figure 3.11 shows a sound clip in the time domain (top) and in the frequency domain (bottom). The lowest pale strip in the frequency domain shows the fundamental resonance frequency and the lines above, its multiple harmonics. Voice Communications Time (s) Time (s) Time (s) Time (s) Figure 3.10 Three waveforms (a, b, and c) with frequencies of 5, 15 and 25 Hz, and their sum (d) The bandwidth of a signal is measured in the baseband, which is the frequency components naturally produced by a source. Modulation and signal processing may increase a 