MODULATOR HAVING MODULATION FACTOR TRANSITION CORRECTING FUNCTION

PROBLEM TO BE SOLVED: To provide a modulator for correcting the transition of a modulation factor with the frequency change of a carrier wave signal. SOLUTION: In the modulator of a direct modulation system, the gain of a variable gain amplifier to pass a modulated signal is controlled by the control output voltage of a PLL for determining the frequency of the carrier wave signal. Besides, the gain of the variable gain amplifier can be controlled with a frequency dividing ratio set to a frequency divider inside a PLL circuit as well. Further, a number of varactor diodes for direct modulation to be connected in a resonance circuit inside a VCO circuit can be varied with the control output voltage or frequency dividing ratio as well.