Radio receiver having phase locked loop and automatic frequency control loop for stably maintaining local oscillator frequency of voltage-controlled local oscillator

A radio receiver comprising:

• receiving circuit means receiving a broadcast signal and recovering an audio information signal from said broadcast signal;
• a voltage-controlled variable-frequency oscillator serving as a local oscillator to produce a local oscillator signal, for causing said receiving circuit means to be tuned to said broadcast signal;
• tuning detecting means coupled with said receiving circuit means for detecting the tuning state of said receiving circuit means;
• a phase locked loop adapted for connection to said voltage-controlled oscillator for controlling the frequency of said local oscillator signal;
• an automatic frequency control loop adapted for connection to said voltage-controlled oscillator for controlling the frequency of said local oscillator signal;
• control circuit means for selectively coupling said phase locked loop and said automatic frequency control loop to said voltage-controlled oscillator in response to said tuning detecting means, said control circuit means coupling said automatic frequency control loop to said voltage-controlled oscillator to maintain the frequency of said local oscillator signal under the control of said automatic frequency control loop when the tuning state is at a predtermined condition, and coupling said phase locked loop to said voltage-controlled oscillator to maintain the frequency of said local oscillator signal under the control of said phase locked loop when the tuning state is not at said predetermined condition;
• a muting circuit connected with said receiving circuit means;
• a muting circuit control means for controlling said muting circuit connected to said tuning detecting means, said muting circuit control means disabling said muting circuit when the tuning state is at said predetermined condition and enabling said muting circuit when the tuning state is not at said predetermined condition;
• a muting switch which operates in such a manner that the control of said muting circuit control means is enabled when said muting switch is in a first state, and that the control of said muting circuit control means is disabled when said muting switch is in a second state;
• and
• means responsive to said muting switch for causing said control circuit means to couple said phase locked loop to said voltage-controlled oscillator to maintain the frequency of said local oscillator signal under the control of said phase locked loop when said muting switch is in said second state.