Given the requirement for a line-of-sight link operating over a sea path and having established the clearance at the horizon over the appropriate range ofk-values using standard procedure, a method is derived for determining the optimum spacing for worst case conditions between receiving antennas where dual space diversity is employed to reduce 2-path fading. The means of calculating the minimum received signal, i.e. the deepest fade possible with destructive interference in the 2-path mode, is also included; as a check on performance if the optimum spacing cannot be realized or where the optimum value is used and the worst case conditions assumed in this determination do not apply in practice.Programs for these calculations are included which run on TI58 or TI59 pocket calculators. A third program for the calculation of Fresnel zone numbers (cubic equation solution) is included. The method is valid for any frequency band in which line-of-sight criteria apply and 2-path propagation occurs.Although consideration of the probability of occurrence of any particular propagation mode lies outside the scope of this paper, it is found that the correct 2-path diversity spacing also provides substantial protection in other adverse propagation circumstances.