Tuning demodulator for digitally modulated rf signals

Abstract

A tuning demodulator for digitally modulated signals tunes and detects a desired RF signal by an I/Q detection circuit and a tuning oscillation circuit composed of a PLL synthesizer having an output frequency close to the desired RF signal, and being provided with electrical or mechanical signal separating components to suppress the leaked output power from the tuning oscillation circuit. The signal separation components include an arrangement of circuits inside a metallic case, a metallic partition board, and an arrangement of power supply terminals. When the tuning demodulator detects a frequency error by a frequency error detection circuit, it adjusts a voltage-controlled reference oscillator that gives the PLL synthesizer an exact frequency reference, and hence it prevents deterioration of the bit error rate of the detected signals. Further, an error correction circuit can be added to compensate the fluctuations in characteristics of constituent parts.