Simulcast Shortwave Frequency Source Design And Research

In modern electronic communication systems, frequency synthesis technology has been used widely. Frequency synthesizer as a core component of electronic devices, its performance has a direct impact on the overall performance of the system.The PLL has been more concerned for a long time. PLL has a good narrow-band tracking performance, and thus based on the principle of phase-locked PLL frequency synthesizer technology has a wide range of output frequency band, spurious rejection performance and the output frequency with a frequency consistent with the reference frequency characteristics.With a GPS reference signal, the project uses PLL frequency synthesis techniques to achieve synchronization of the synchronous carrier. At First, introduce several basic methods of frequency synthesis and make a explanation of the selection of the reference frequency sources. And then, the technology and the structure of PLL is mainly analyzed, also the frequency synthesizer specifications are briefly introduced. According to the technical requirements of the technical targets of the system, we choose a digital phase-locked loop chip with a excellent performance after the system solution is selected and verified, then a frequency synthesis system which is directly controlled by a chip of LPC2148 based on ARM microcontroller has been designed. In addition, the circuit board is fabricated and the debug is completed. All the functional modules of the hardware have been described in details especially about the DPLL principle and the filter circuit design. The circuit can provide a sine wave output and also a square wave output. The software is focused on the use of digital phase-locked loop controlling and the VHDL design of the CPLD co-processor.Finally, the system test results are obtained and some suggestions and recommendations for improvement are proposed.