te needs to have connectiv- ity, SO there is likely to be some compromise on the height of the site to be selected in a given region. Sometimes, the important sites chosen by the radio planners are low or are between high building structures, and in such cases repeaters are used by transmis- sion planners. These repeater sites are usually on high buildings having only transmission equipment. TRANSMISSION NETWORK PLANNING AND OPTIMISATION Line-of Sight Survey Connectivity is a very important criterion for site acceptance for both transmission planning engineers and radio planning engineers. Transmission planners make sure that one site is visible from the next site. It is not sufficient for one site merely to be visible from another but LOS criteria must be clear before a site is accepted. This process may also lead to construction of the path profile, especially with longer hops. This clearance criterion is based on the concept of a Fresnel zone. A typical Fresnel zone and path profile are shown in Figure 3.7. d (km) Site B Figure 3.7 Fresnel zone and path profile analysis 3.3.6 Radius of the Fresnel Zone Typically, the Fresnel zone can be defined as an area that is covered by an imaginary ellipsoid (a three-dimensional ellipse, as shown in Figure 3.8) drawn between the transmitting and receiving antennas in such as way that the distance covered by the ray being reflected from the surface of the ellipsoid and reaching the receiving antenna is half a wavelength longer than the distance covered by the direct ray travelling from the transmitting to the receiving antennas, i.e. d1 + d2 = a/2. Figure 3.8 Radius of the Fresnel zone The Fresnel zone is dependent upon two factors: frequency of transmission and the distance covered. Mathematically, the radius of the Fresnel zone can be calculated as: 12.75(d*d2/f*D) (3.1) where F1 is the radius of the first Fresnel zone, f is the frequency of the transmitted signal in GHz, and D, d1 and d2 are distances in km (as shown in Figure 3.8). In most cases, the radius of the firs