Varactor Diode Frequency Modulator

The varactor frequency modulator is as shown in the figure. The transistor is 3DG6 and the varactor diode is 2. Think about 1×2.
    The junction capacitance of the varactor diode is part of the oscillator oscillation circuit . The junction capacitance changes with the modulation signal, the total capacitance of the loop also
changes with the modulation signal, and the oscillation frequency will also change with the modulation signal. As long as the characteristics and working state of the varactor diode are appropriately selected,
the change in the oscillation frequency of u and f can be approximately linearly related to the modulation signal, thereby achieving frequency modulation. The relationship between the instantaneous frequency of the varactor frequency
    modulator and the modulation voltage is determined by the oscillation circuit. Due to different connection methods, the impact of varactor diodes on the oscillation frequency of the loop is also different; the methods of connecting varactor diodes to the oscillation circuit are divided into two types: full connection and partial connection.