r this is that different uses require different types of lines. Remember that in Equation 2.2.1 repeated To infinity here for convenience Z = 13810g10(D/d)/Je: or matched termination the dimension of the variables can be changed to produce the desired impedance. 75 S - This type of cable is favoured by the television industry because it provides a close match to the impedance (73.13 (2) of a dipole aerial. Most TV Fig. 2.2-11 Pulse propagation in a transmission line. The behaviour of a pulse travelling along an infinitely long transmission line is very similar to the example you were given in Section 2.2.2.2 concerning sound travelling down an infinitely long tunnel except that this time instead of voice sounds, consider the sound to originate from a single drum beat or pulse. You will no doubt remember from earlier work that a pulse is a waveform which is made up from a fundamental sinusoid and its harmonics combined together in a precise amplitude, phase and time relationship. Transmission lines CHAPTER 2.2 line (top left hand corner) a voltage source (Vs) produces amplitude reduction per unit length. Its unit is called the the single pulse shown in Figure 2.2-11. The waveforms neper and loss (dB) = 8.686 nepers. shown at various planes (plane 1, plane 2, plane 3) on the line illustrate three of the main properties of signal Example 2.2.6 propagation along a transmission line: A transmission has a loss of two nepers per kilometre. propagation delay - the pulse appears at each succes- What is the loss in dB for a length of 10 kilometres? sive point on the line later than at the preceding point; Given: Attenuation constant (a) = 2 nepers per km. attenuation - the peak value of the pulse is attenu- Required: Loss in dB for a length of 10 km. ated progressively; waveform distortion and frequency dispersion - its Solution shape differs from its original shape at successive If 1 km represents a loss of 2 nepers, then 10 km = 10 X points. 2 = 20 nepers. Therefore loss = 8.686 X 20 = 173.72 dB 2.2.8.2 Propagation delay