| 摘要 |
PURPOSE:To extend the variable range of an oscillation frequency without losing the stability of oscillation, by connecting a feedback capacitor between an output terminal of a transistor (TR) and a cathode of a varactor diode for tuning. CONSTITUTION:A local oscillation circuit consists mainly of a tuning coil 1, tuning varactor diode 2 to continuously change the oscillated frequency, a tracking capacitor 3, oscillating TR5 and feedback capacitor 7, as shown in figure. The feedback capacitor 7 is not connected between an emitter and a collector of the TR5, but connected between an output terminal of the TR5 and a cathode of the diode 2. Thus, the capacitor added in parallel with the diode 2 is constituted small as a coupling capacitor 4 and a capacitance between the collector and the base of the TR5. Since the oscillation circuit shown in figure has a large ratio of change in oscillating frequencies and the capacitor 7 can be increased, the oscillation can be stabilized. |
