Receiver input circuit with high signal=to=noise ratio - has mixer operated by VCO over control loop with coordinated frequency and phase

摘要

The input circuit replaces parametric receiver input stage circuits and has a higher signal-to-noise ratio in front of the demodulator. It consists of a parametric downstream mixer and a series-connected demodulator. The mixer is supplied by a V.C.O. synchronised in frequency and phase via a control circuit so that the following terms are met: p - 2z and p-z-3z, where p is the voltage control oscillator frequency and z the intermediate frequency. The mixer is terminated by real resistor at the mirror frequency to enable power amplification. Pref. a series-connected low noise preamplifier is provided for the mixer. For microwave range the parametric mixer may be used as a preamplifier at the signal frequency. With frequency modulated input signal the demodulator forms a phase detector, between which and the mixer, is incorporated an i.f. amplifier. A low pass filter is connected at the output of the demodulator, and the l.f. can be tapped at the same.