倒计数法测频的原理与实现

Principle and realization of frequency measuring with countingdown method

从雷达发射机耦合出来的发射脉冲信号经下变频、滤波后由比较器转换成中频方波信号,倒计数测频电路用该方波信号的Nx个周期形成计数区间,在此计数区间内使用F161高速计数器对100 MHz的标准方波进行计数,单片机根据计数结果计算出中频方波信号的频率和发射频率。该电路在雷达发射脉冲持续期间对其发射频率进行实时的快速测量,已成功用于某型米波警戒雷达的自动频率控制系统中。

The intermediate frequency signal,which is generated by down conversion of radar transmission pulse,is settled as square wave through the signal processing circuit; in N cycle of the unknown square wave of this frequency,the frequency measurement circuit with counting down method uses the counter and the time-sequence control circuit consisting of TTL integrated circuit,such as F161 and LS221,to count the standard pulse exported by homothermal crystal with high stability and then load the result in single chip in order to obtain the frequency measuring result. This frequency measuring circuits can rapidly and timely measure the transmission frequency during the constant radar transmission pulse and has been successfully applied in automatic frequency control system of meter wave warning radar.