Design of Local Oscillator Based on DDS of High Performance Short-Wave Receiver

Local oscillator based on direct digital synthesizer (DDS) of radio frequency front-end part of all digital short-wave receiver is introduced in this paper. At first the concept of both local oscillator phase noise and spurious signals at the output of DDS are simply described, as well as their effects on receiver performance. And then take some measures to improve the local oscillator performance, such as using multi-frequency circuit to improve the purity of frequency spectrum, using tracking filter to degrade harmonics, using gain control circuit to remain constant in local oscillator amplitude in the desired frequency range.