Frequency modulation system

A frequency modulation system comprising:

• first means including a first variable frequency oscillator, a frequency divider for frequency dividing the output frequency of said first variable frequency oscillator, a reference frequency oscillator, and a first feedback circuit in which the output frequency of said reference frequency oscillator is compared in phase with that of said frequency divider and the result of the phase comparing is fed back to said first variable frequency oscillator through a first filter for controlling the output frequency of said first variable frequency oscillator;
• second means including a second variable frequency oscillator, a fixed frequency oscillator, means in which the output frequencies of said second variable frequency oscillator and of said fixed frequency oscillator are mixed in a mixer thereby to obtain a difference frequency between said both frequencies, and a second feedback circuit in which said difference frequency is compared in phase with the output frequency of said first variable frequency oscillator and the result of the phase comparing is fed back to said second variable frequency oscillator through a second filter for controlling the output frequency of said second variable frequency oscillator;
• and
• third means in which the output frequency of said fixed frequency oscillator is frequency-modulated by the frequency of a modulating signal thereby to obtain a frequency-modulated wave from said second variable frequency oscillator.