Radio receiver for fsk signals - has local oscillator with output fed to D=flip=flop via two mixers and two limiting amplifier stages (DK 4.2.80)

摘要

The simple radio receiver is for use in eg. a paging system. RF signals from the aerial are mixed in two high gain mixers with local oscillator signals which are in quadrature and which are at the nominal centre frequency of the input signal. The output from the mixers are low-pass filtered so as to extract the difference frequency. The low-pass filter bandwidth is equal to the sideband width of the RF signal. Baseband signals from the filters are now amplified in high gain limiting amplifier stages which deliver fully symmetrically limited outputs at logic level to a D-type flip-flop.