| 摘要 |
A superheterodyne receiver of a scanning type, comprising a high frequency amplifier, a mixer, a local oscillator, an interdmediate frequency amplifier, a detector, an audio frequency amplifier, a loud speaker, and an automatic scanning/manual scanning selecting switch, said local oscillator comprising a digital frequency synthesizer comprising a voltage controlled oscillator, a programmable frequency divider for dividing the frequency of the output from the voltage controlled oscillator, a reference oscillator, a random access memory for storing the information concerning the rate of the frequency division by the frequency divider, and a phase detector for phase detecting the frequencies of the outputs from the reference oscillator and the frequency divider for providing a control voltage to said voltage controlled oscillator, said receiver further comprising an astable multivibrator for generating pulses for scanning the frequencies of the receiving bands, a counter for counting the pulses from the astable multivibrator, a decoder for decoding the count output from the counter, a plurality of light emitting diodes correspondingly coupled to the decoder output, a plurality of switching transistors connected to a plurality of bit parallel outputs of the random access memory, a plurality of switches for presetting in the random access memory the information concerning the rate of frequency division by the frequency divider corresponding to a predetermined channel, a squelch circuit responsive to a noise detected output obtained when the said detector detects a noise for disabling the audio frequency amplifier, a plurality of undesired channel setteing switches for presetting a channel reception of which is not desired, and a switching transistor responsive to the reception of the frequency corresponding to the channel as set by the said undesired channel setting switch for providing a potential for forcibly enabling the said squelch circuit for disabling the audio frequency amplifier.
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