Design and realization of local oscillator for VHF survival receiver

Local oscillator is an important device for survival radio system receiver. In this paper, a simple design and flexible configuration, local oscillator using DDS (Direct Digital Frequency Synthesis) technology has been designed and realized. Concerning with double conversion superheterodyne RF Front-End for the receiver, the local oscillator is to generate two channel sinusoidal signals whose frequencies are 130 and 70 MHz separately. The local oscillator consists of a CPLD (complex programmable logic device), two DDS chips, two crystal oscillators, and two low pass filters. The CPLD serving as the controller controls the operation of two DDS chips. The control parameters are stored in the UFM (User Flash Memory) block embedded in the CPLD. The complexity of the circuit is reduced effectively by synchronous serial communication protocol scheme applied between the CPLD and two DDS chips. Simulation and experiment results show that the logic circuit design of the controller is correct and the local oscillator has a good performance.