Phase-locked loop (PLL) is able to track the input phase of the closed-loop automatic control system. In all areas of radio technology has been widely used.In this paper, the design of a PLL FM communications systems. PLL paper introduces the basic working principle and use of technology for phase-locked FM modulation and demodulation principle, described in detail with CD4046 and NE567 phase-locked loop chip for the design of modulation and demodulation method of circuit design, The test results proved that the design of the rationality and correctness of a certain application of the value of this article
