| 摘要 |
An FSK receiver includes first and second channel paths to which the received FSK signals are applied. Each channel path includes a mixer circuit, a low-pass filter connected to the mixer circuit, and a limiting amplifier connected to the low-pass filter. A voltage-controlled oscillator generates a local carrier and a phase shifter applies its output to the mixer circuits with a 90.degree. phase difference therebetween. A frequency detector is coupled to one of the limiting amplifiers for generating a signal representative of the deviation frequency minus the offset frequency of the received FSK signal. An average circuit detects an average value of the signal from the frequency detector. A comparator circuit detects whether the frequency representative signal lies in or outside of the neighbourhood of the average value. A ramp voltage of constant amplitude is periodically generated if the signal is detected as lying outside of the neighbourhood and maintained at an instantaneous value if the signal is detected as lying in the neighbourhood. The voltagecontrolled oscillator is responsive to the ramp generator to control the frequency of the local carrier in search of the transmitted carrier frequency.
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