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快跳频(FFH)系统的接收机,在由本振跳频信号超前接收信号的起始条件至同步止分三个阶段与发射机同步。第一阶段中,在每一 FFH 周期内检测跳频接收信号和本振跳频信号的差频以作中频。将 FFH 周期分组,如果所有周期组均有中频,则第一阶段便结束。但是,每组周期若不满足这个条件,本振频率推迟一个 FFH 周期。在第二阶段中,将两个在半个 FFH 周期内的中频相比较,以确定是否在超前或滞后半个多 FFH 周期时仍有中频存在,同时调节本振信号相位,直至本振跳频信号和接收信号的相位差小于预定 FFH 周期较小部分为止。第三阶段中,分别将两个附加的本振信号(它们与本振信号相同,但相位分别以同样小部分 FFH 周期超前与滞后本振信号)与本振信号相混频,并比较其差频,进行细调本振信号相位,使之与这两个信号产生的中频相位大体上相等,为更精确调节,可附加与第三阶段相似的第四阶段。
The FFH system receiver synchronizes with the transmitter in three stages, starting from the LO signal and receiving the signal in advance, to the synchronization stop. In the first stage, the difference frequency of the frequency hopping received signal and the local oscillator frequency hopping signal is detected as the intermediate frequency in each FFH cycle. The FFH periods are grouped, and if all the period groups have an IF, the first phase ends. However, if each cycle does not satisfy this condition, the local oscillator frequency is delayed by one FFH cycle. In the second phase, two intermediate frequencies in a half FFH period are compared to determine whether there is still an intermediate frequency in the leading or lagging half-many FFH periods while the local oscillator signal phase is adjusted until the local oscillator frequency hopping The phase difference between the signal and the received signal is less than the smaller portion of the predetermined FFH period. In the third stage, the two additional local oscillator signals (which are the same as the local oscillator signal but each phase leads and lags the local oscillator signals with the same small fraction of the FFH cycle) are respectively mixed with the local oscillator signal and compared with each other The phase of the local oscillator signal is fine-tuned so as to be substantially equal to the phase of the intermediate frequency produced by these two signals. To be more precisely adjusted, a fourth phase similar to the third phase may be added.