ave. Waveforms may have other equipments and do not need high voltages. Semi- shapes such as square waves, ramps, etc., as will become conductor devices do also have a considerable role in apparent later. transmitter drives, audio circuits and in control systems. A sine wave is illustrated in Figure 2.5-1 and is shown In the latter application, sophisticated logical control with the 'Y' axis denoted arbitrarily in amplitude (A). circuits are easy to achieve and occupy the smaller The term amplitude is used to refer to the magnitude of volumes attributable to the small size of transistors and the voltage or current. integrated circuits. The instantaneous amplitude (amplitude at a specified With the vast increase of terrestrial and satellite point in time) can be read from such a diagram and will broadcasting and communications, and the enormous be found to follow a sine curve, i.e. it is equal to the number of mobile phones now in use, homes, work and maximum amplitude (A) multiplied by the sine of the recreational places are irradiated by a vast number of corresponding angle. electromagnetic signals. Many are intended to operate Hence at 0° and 180° the instantaneous amplitude is receiving equipment, most of which are at very low levels zero. Similarly at 90° and 270° the instantaneous because the high sensitivity of receivers does not amplitude is at the maximum A but since the sine of necessitate large signals. Mobile phones do however 270° is negative the polarity and hence the direction of communicate both ways and thus incorporate trans- current flow has reversed. This diagram is basically mitters and receivers. As usage increases there is pressure applicable to any simple AC waveform. One of the for the use of more frequencies such that governments factors which distinguishes such waveforms is the time now sell licences to use parts of the RF spectrum. duration of one complete cycle (T) in Figure 2.5-2 and Some radiation is unintentional, resulting from the another the frequency (f). leakage of energy from 