DIVERSITY RECEIVING SYSTEM WITH A VOLTAGE CONTROLLED OSCILLATOR COUPLED TO A CRYSTAL CONTROLLED OSCILLATOR IN AT LEAST ONE CHANNEL

摘要

In a diversity reception system in which each channel includes a local oscillator for converting the received signals to a common I.F., at least one of the local oscillators includes a crystal controlled oscillator and a voltage controlled oscillator coupled to the output of the crystalcontrolled oscillator, and phase control means are coupled to each of the channels to control the crystal-controlled oscillator and the voltagecontrolled oscillator to maintain the I.F. signals in a predetermined phase relationship for subsequent combining. As shown in Fig. 1, diversity channel 2 includes a mixer 3 and a local oscillator 5 comprising a crystal-controlled oscillator 7 and associated frequency multipliers synchronizing a voltage controlled oscillator 8 which is coupled via a multiplier 9 to the mixer 3, the diversity channel 2n including a mixer 3n and a fixed frequency local oscillator 5n. The outputs of the I.F. amplifiers 4, 4n are supplied to a phase comparator 6 which via a low-pass filter 10 " pulls " the frequency of oscillator 7 and via a high-pass filter 11 controls the phase of oscillator 8. By this means the signals in the two channels are brought into phase for combining at 12. In a modification, Fig. 3 (not shown), both local oscillators are as oscillator 5 and are controlled in antiphase by signals from the phase comparator. In a further arrangement which is suitable for any number of diversity channels, Fig. 4 (not shown), each local oscillator is controlled in the manner of oscillator 5, Fig. 1, and the I.F. amplifiers are connected via respective buffer amplifiers to a common output line. Each channel includes a phase comparator comparing the common output signal with the output of the corresponding I.F. amplifier to effect the required phase control of the local oscillator.