 used to plot the path and straight lines are used instead of curved lines, making plotting of the path profile easy. The path profile is drawn on a linear graph paper, where a straight line is drawn from the transmitter to the receiver, giving tangential clearance of equivalent obstacle heights. Bending of the radio beam is represented by an adjustment to each obstacle height by an equivalent earth bulge (calculated from Equation (3.22)), as shown in Figure 3.42. Example. Draw a path profile for a 30 km terrain. The terrain profile at the standard atmosphere condition (k = 4/3) is drawn for a hop between sites A and B in such a way that radio wave propagation is shown as a straight line. The height of the terrain after every 2 km is given in Table 3.9. Based on this information, the earth bulge should be calculated for each of the distance points men- tioned. On top of that clearance is added, which will take into account the trees, buildings, etc. Depending upon the region's obstacle heights, the clearance factor can be changed. Once this is done, a straight line is drawn and the antenna heights are found. In this case, an antenna at a height of 14 m at both the sites would be sufficient (the maximum height to be cleared is 23.1 m) (see Table 3.10). 3.4.5 Link Budget Calculation The link budget calculation is one of the most important aspects of microwave engineering. Through link budget calculations, the amount of power received at the receiving antenna is calculated, which forms the basis of calculation of fade margin and availability. Before link calculations are discussed it is important to understand the term 'free space loss'. d (km) Figure 3.42 Path profile Transmission Network Planning and Optimisation Table 3.10 Results of drawing a path profile D [km] Height [m] d2 [m] k-factor Earth bulge Cleaarance Total height Free Space Loss Consider an isotropic antenna radiating in free space (as shown in Figure 3.43). The point source is located in the centre of the sphere. As the antenna is isotropic, it can b