Principle and Realization of Frequency Measuring with Countingdown Method

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, a digital frequency measurement module, can rapidly and timely survey the transmission frequency during the constant radar transmission pulse and has been successfully applied in a self-adaption frequency control system of meter wave warning radar.