can be removed by good system design. Inter-channel interference consists of interferences caused by co-channel and adja- cent channels. Co-channel interference means that some signals from identical frequency bands are reaching the microwave antenna. However, co-channel interference can only be cross-polar, i.e. the signals will be 90 degrees out (e.g. one is horizontally polarised while other is vertically polarised). Adjacent-channel polarisation means that both the frequency bands of both the signals are next to each other (e.g. one can be 18.1-18.4 while the other is 18.2-18.6 GHz). Unlike co-channel interference, adjacent-channel interference can be both co-polar and cross-polar. These are shown by signals 1, 3 and 4 in Figure 3.17. Using non-consecutive frequency bands in the same or adjacent links can prevent this kind of interference. Inter-hop interference is caused by an undesired signal arriving at the receiving antenna. Using different frequency spots at potential sources of interference can prevent this kind of Figure 3.17 Sources and types of interference: (1) co-channel/adjacent channel from dif- ferent hops; (2) opposite hop front-to-back reception; (3) adjacent channel, same hop; (4) cross-polarisation, same hop; (5) front-to-back radiation; (6) over-reach; (7) terrain reflection DETAILED TRANSMISSION NETWORK PLANNING interference. Techniques such as using different polarisation in subsequent links, and tilting of antennas, are remedies. Sometimes interferences are detected in a network, even though frequency plans are perfect. This may be due to possible reflections that might be taking place in the network. In these kinds of situations, again, techniques like antenna tilting, or reducing power to the transmitting antenna (interfering source), can be used. Example 4: Interference Calculation (Over-reach): This example calculates the signal to interference ratio (S/I) and threshold degradation due to over-reach interference. Two links are assumed to be operating at the same frequency. The links,