We report passive harmonic mode locking of a soliton Yb fiber laser at repetition rates continuously scalable up to 1.5 GHz. The laser generates transform-limited 500 fs pulses, with pulse energies of 30-100 pJ. At the 31st harmonic (1.3 GHz), the cavity supermodes are suppressed by 35 dB, and the pulse-to-pulse timing jitter is 6 ps.