lcordia. CONCEPTS IN TRANSMISSION TRANSPORT Terminal Repeater Repeater station Terminal station station with drops and inserts station DEMUX DEMUX DEMUX Channel Exchange A Exchange B Exchange C Channel Channel Subscribers connecting radio trunks system trunks trunks Figure 9.4 Simplified functional block diagram of the LOS microwave system shown in Figure 9.2. 2. Siting based on propagation advantages (or constraints) only versus colocation with exchange (or corporate facility) (saving money for land and buildings). 3. Choosing a method of feeding (feeders3: by light-route radio, fiber-optic cable, and wire-pair cable. 9.2.3.3.2 Calculation of Tower Heights. LOS microwave antennas are mounted on towers. Formulas (9.1) allowed us to calculate a rough estimate of tower height. Towers and their installation are one of the largest cost factors in the provision and installation of an LOS microwave system. We recommend that actual tower heights do not exceed 300 ft (~90 m); otherwise, additional expense will be required SO that the tower meets twist and sway requirements. Of course, the objective is to keep the tower height as low as possible and still maintain effective communication. The towers must be just high enough to surmount obstacles in the path. High enough must be carefully defined. What sort of obstacles might we encounter in the path? To name some: terrain such as mountains, ridges, hills, and earth curvature- - which is highest at midpath- buildings, towers, grain elevators, and SO on. The path designer should consider using natural terrain such as hill tops for terminal/relay sites. She/he should also consider leasing space on the top of tall buildings or on TV broadcast towers. In the following paragraphs we review a manual method of plotting a path profile. From a path profile we can derive tower heights. Path profiles may be prepared by a PC with a suitable program and the requisite topological data for the region stored on a disk. 3 Here the word feeders refers to feeding a mainline trunk radio syste