Modulation systems

In combination:

• a first frequency source for producing a carrier signal;
• a second frequency source for producing a frequency deviating intermediate frequency signal;
• and
• apparatus for deviating the frequency of said carrier signal in accordance with the deviations of said intermediate frequency signal comprising:
• modulator means for varying the frequency of said carrier signal in accordance with a modulating signal;
• first mixer means for providing sum and difference frequency signals of the product of the modulated carrier signal and the frequency deviating intermediate frequency signal;
• filter means coupled to said mixer means and resonant at a predetermined one of said sum and difference frequency signals for providing a carrier control signal having a phase error component proportional to the deviation of said predetermined one of said sum and difference signals from its predetermined value;
• second mixer means for mixing said carrier control signal with said modulated carrier signal to produce an intermediate frequency control signal having a phase error component proportional to the deviation of said predetermined one of said sum and difference signals from its predetermined value;
• and
• means for comparing said intermediate frequency control signal with said frequency deviating intermediate frequency signal to provide said modulating signal.

Apparatus for deviating the frequency of a carrier signal in accordance with the deviations of an intermediate frequency signal comprising:

• modulator means for varying the frequency of said carrier signal in accordance with a modulating signal;
• first mixer means for providing sum and difference frequency signals of the product of the modulated carrier signal and the frequency deviating intermediate frequency signal;
• filter means coupled to said mixer means and resonant at a predetermined one of said sum and difference frequency signals for providing a carrier control signal having a phase error component proportional to the deviation of said predetermined one of said sum and difference signals from its predetermined value;
• second mixer means for mixing said carrier control signal with said modulated carrier signal to produce an intermediate frequency control signal having a phase error component proportional to the deviation of said predetermined one of said sum and difference signals from its predetermined value;
• means for comparing said intermediate frequency control signal with said frequency deviating intermediate frequency signal to provide said modulating signal;
• and
• means for varying the resonant point of said filter means in accordance with the direct current component of said modulating signal.