We demonstrate that the lin-par-lin Ramsey coherent population trapping Rb clock using a dispersion detection technique has a promising performance. We theoretically and experimentally investigate the signal-to-noise ratio of the Ramsey spectrum signal by varying the relative angle of the polarizer and analyzer as well as the magnetic field. Based on the experimental results, the optimized relative angle and magnetic field are determined. This kind of atomic clock is attractive for the development of compact, high performance vapor clock based on CPT.