RECEIVER FOR FREQUENCY-MODULATED RF SIGNALS

摘要

An FM receiver has a first pair of signal mixers for receiving an RF signal and a local oscillator for providing a signal to said mixers at a frequency near the center frequency of the received signal. A phase shifter shifts the phase of the local oscillator signal to one mixer by 90 DEG . The outputs of the first pair of mixers are connected to low pass filters having cut-off frequencies equal to approximately one-half the bandwidth of the received signals. A second pair of signal mixers receive the filtered signals and an oscillator signal at a frequency equal to at least twice the cut-off frequency of the low pass filters. The oscillator signal to one of the mixers is phase shifted 90 DEG . The outputs of said second pair of mixers are added together, amplified, limited and thereafter demodulated to provide an audio signal. Automatic frequency control is also provided for the local oscillator.