A radio over fiber (RoF) transmission system based on a gain-switched laser as an optical comb source is proposed and demonstrated. 12.5 Gb/s 16 quadrature amplitude modulation (16 QAM) signal generation and transmission over 25 km standard single-mode fiber is experimentally demonstrated using a 60 GHz carrier. The phase noise of the 60 GHz signal resulting from the beating of two partially phase uncorrelated optical tones is theoretically studied and experimentally investigated. Phase noise comparison with different linewidth comb sources is implemented in the proposed RoF system, and the performance of the various systems with different levels of phase noise is presented. © 2012 IEEE.