A spectral emission mask for digital tropospheric scatter transmission

A spectral emission mask definition for high power digital radio transmission is proposed. Developed for use in the specification of digitalized ACE high troposcatter links, it is offered for consideration by industry and frequency planning authorities. Similar in form to the FCC mask definition for digital LOS radio, the proposed definition is believed to be a reasonable compromise between minimizing interference into adjacent radio channel allocations and avoiding the imposition of costly constraints upon the manufacturers and operators. Computer simulations supported by spectral measurements at 10 kW have shown that well designed filtering (with negligible intersymbol interference) before the high power amplifier is very effective in reducing out of band emission, and that the proposed mask can be satisfied with a signal having a bandwidth utilization efficiency of 1.6 bit/s/Hz when operating at 2 dB below saturation of the klystron amplifier.