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Generation of stable micro or radio waves by frequency down-conversion has always been a challenging but rewarding task in radio over fiber systems. In this letter, a novel method for such a generation using a short-cavity fiber laser is demonstrated. For this purpose, an all-fiber laser is designed to have two stable longitudinal laser modes, each of them having two orthogonal polarization modes. Hence, four microwave signals, two in 1.2 GHz range and the other two in 14 GHz range, and one radio wave signal were generated by beating these lasing modes on a square law detector. Various measurements show high level of stability in generated micro/radio waves because they originate from the single laser cavity. According to the authors' knowledge, this is the first demonstration of the dual longitudinal mode operation of a short-cavity fiber laser for down-conversion from optical frequency directly to radio frequency.