Information Bandwidth of Tropospheric Scatter Systems

A set of design curves of peak intermodulation distortion due to frequency selective fading, as a function of information bandwidth, is derived for tropospheric scatter systems. These curves are applicable to systems frequency-modulated with frequency-division multiplexed telephone and telegraph channels. A two-ray tropospheric scatter model was selected in order to derive general results. This, however, restricts the use of the design curves to the region where the information bandwidth is less than the propagation bandwidth. Equations for intermodulation distortion are evaluated for parameters normally encountered in tropospheric scatter systems. A method of obtaining a probability distribution of the distortion is indicated, and an example is worked out in detail. The intermodulation distortion due to frequency selective fading will exceed the thermal noise in some systems, and should be taken into consideration when designing tropospheric scatter systems.