Gain maintenance apparatus for use with a high gain amplifier incorporated in a closed loop feedback system

Phase-lock loop apparatus comprising, in combination:

• phase detection first means;
• voltage controlled oscillator second means;
• third means, including high gain amplifier means and phase-lock detection means, for providing an output first signal when a lack of phase-lock of the loop is detected;
• fourth means connecting said first, second and third means in a phase-lock loop feedback arrangement where said high gain amplifier means comprises a direct part of the feedback path of the phase-lock loop and is connected to supply signals to drive said voltage controlled oscillator second means;
• sweep signal supplying fifth means, connected to said second and third means for supplying a sweep second signal to said second means while receiving said output first signal;
• and
• signal centering sixth means, connected in a signal feedback relation from an output to an input of said high gain amplifier portion of said third means and including a signal input means connected to said third means for receiving said first signal and further including first and second reference potentials, for maintaining the voltage output of said high gain amplifier means at a value intermediate said first and second reference potentials when the phase-lock loop is not in a locked condition.