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Present day service requirements dictate greater emphasis on reliability as a system design parameter and performance measure. In this paper reliability is defined and objectives are presented for a 10-hop 250-mile short-haul microwave radio relay system. A general discussion of the sources of unreliability (outage) precedes a section on possible techniques of minimizing their effects. This is followed by a detailed reliability analysis utilizing outage probability factors based on experience, field data, and judgment. A comparison is then made with reliability data on working systems. From these figures the conclusion follows that some form of diversity protection is a necessity if the proposed reliability objectives are to be met. In particular it appears that the use of a solidstate 6-Gc/s-11-Gc/s frequency diversity system with per hop switching will allow the economical attainment of the reliability objectives. In addition, this system will permit maximum utilization of both a congested portion of the frequency spectrum and a portion not otherwise usable in some areas because of rain attenuation.