| 摘要 |
PURPOSE:To stop the sweepage at the optimum tuning point by lowering the voltge by the fixed valve at the sweep stop time to eliminate occurrence of the oversweep through the high-speed sweepage with reduction of the integration constant at the channel selection start time and through the low-speed sweepage with increases integration constant near the desirable channel-selected station. CONSTITUTION:Electronic tuner 1 possesses the voltage control type local oscillator, and tuning voltae sweep circuit 8 generates the pulse which increases with the time lapse to apply it to the integrating circit. Thus, the DC voltage is obtained at the output side. While the oscillation output of the local oscillator in tuner 1 detects (3) elastic surface wave filter SAW2 and its output, and then counts (7) the output frequencies of the output to stop the sweepage of circuit 8 after counting. Thus, the channel selection is carried out. In this case, the integration constant of the integrating circuit is switched, the high-speed sweepage is carried out with reduced integration constant at the channel selection start time, the low-speed sweepage is given with increased integration constant near the desirable channel-selected station, and the voltage is lowered by the fixed amount at the sweep stop time. Thus, the occurrence of the oversweep is eliminated, and the sweep of the tuning voltage can be stopped at the optimum tuning point. |
