IC-725A短波电台本振频率的高稳定度改进

在短波信道探测中,收发系统的本振频差对多普勒频移的测量至关重要.针对短波信道探测系统中IC-725A短波电台原有本振频偏较大的问题,采用锁相环（PLL）频率合成技术,利用铷时钟提供基准参考频率,对IC-725A短波电台的本振信号源进行高稳定度改进.给出PLL中鉴相器（PD）、环路低通滤波器（LF）的设计方案,并用电路实现.研究并给出一种在不影响电台总体性能的情况下将PLL输出的高稳定度本振信号注入到电台中的方法.实验测试结果表明,改造后两部IC-725A短波电台的本振信号的频差在10-4 Hz数量级,完全能满足短波信道探测对电台本振频率精度的要求.

High Stability Improvement of Local Oscillation Frequency of IC-725A HF Transmitter-Receiver

The local oscillation frequency difference between transmitter and receiver is of great importance to the meas- urement of Doppler shift in high frequency（HF） channel sounding. The original local oscillation frequency offset of IC-725A HF transmitter-receiver is too big to measure Doppler shift. Therefore, a method is proposed to improve the stability of local oscillation frequency of IC-725A, which is based on phase-locked-loop（PLL） frequency synthesizing technology. And the ru- bidium clock is used as norm reference frequency source. The design schemes of phase discriminator（PD） and loop low-pass fiher（LF） are provided, which is implemented by circuit. The injection approach of the high stability local oscillation signal output by PLL into IC-725A is given, by which the performance of IC-725A is totally not influenced. The result of test ex- periment shows that the local oscillation frequency difference of two improved IC-725A is at the magnitude of 10.4 Hz, which means that it satisfies the local oscillation frequency precision requirement of HF channel sounding.