| 摘要 |
PURPOSE:To prevent electric power loss, change of the modulation characteristic, and fluctuation of the operation characteristic of PA, by performing output control electronically. CONSTITUTION:The secondary side of transformer 54 is subjected to full wave rectification by diode bridge 57. For the purpose of setting the voltage of the secondary winding to an arbitrary value without loss, the rectified output is caused to pass through low-pass filter 58 and is switched by FET59. By controlling the pulse width (ON duty) of switching, the rectifying voltage is controlled forcedly. The sine wave output of OSC is used as a sample carrier wave and is subjected to pulse width modulation in PWM60 according to voltage drop of resistance 61 provided between PA53 and the earth. When the PA current becomes large, pulse width modulation is performed in the direction where the ON duty of FET59 beomes small, and voltage drop components dependent upon transformer 54 is controlled to make the PA current fixed. As a result, automatic output control is performed, and an approximately fixed output can be obtained at output terminal 56. |
