| 摘要 |
PURPOSE:To solve the problem of the noise interference at the AFT time by selecting the frequency near the transmission frequency desiring reception via the PLL frequency synthesizer and retrieving the transmission wave based on the selected frequency to convert the reception system from the PLL system to the search tuning system. CONSTITUTION:The channel selector of the TV picture receiver or the like possessing the loop forming the PLL frequency synthesizer which generated the local oscillation frequency corresponding to the frequency near the electric wave of the transmission station desiring the reception plus the searth tuning system comprising local oscillator 21, mixer 31 and others. In such channel selector, voltage adder 70 which adds the output of voltage integrator 37 of the search turning system under the fine adjustment possible sweep state at the output of low-pass filter 26 forming the PLL loop. Then the output of adder 70 is applied to oscillator 21 and high frequency amplifier 39, and the PLL is turned to the open loop when the voltage of amplifier 39 reaches the level corresponding to the frequency near the reception desiring frequency. After this, the transmission wave is searched through the search turning system to secure the turning state. |
