Multipath Intermodulation Associated with Operation of FM-FDM Radio Relays in Heavily Built Areas

Microwave FM radio link paths concerning heavily built areas may be found to suffer from high amounts of intermodulation noise caused by multiple reflections on buildings and reflecting obstacles lying alongside the direction of propagation. Little direct information may be gained on these effects using standard techniques for measuring transmission performance. The limitations of those techniques are discussed and some additional ones are proposed allowing a more direct insight into the phenomenon. The results obtained in measurements on a real hop suffering from marked echo effects of this type are reported and discussed.