Color frame lock control for signal reproducing systems

Claim 1

In combination with a magnetic tape system for initially storing and thereafter reproducing a color television signal including horizontal synchronizing pulses and color subcarrier components having color bursts having a given relative position between the leading edge of the horizontal synchronizing pulses and the color burst phase, and including a coarse time base corrector of the type including a first electronically variable delay line having a signal input receiving a composite color signal reproduced by a plurality of magnetic heads on a servocontrolled rotary head drum successively scanning predetermined transverse tracks of a video tape recording transported past the drum at a predetermined speed by a capstan drive under control of a capstan servo, a signal output, and a control input for varying the phase of the video signal passing between the signal input and output in accordance with a first error signal applied to the control input, said first error signal being proportional to the difference in phase between the horizontal synchronizing pulses of said reproduced video signal and a reference horizontal synchronizing pulse signal, said corrector further including a second electronically variable delay line having a signal input receiving the video signal from the signal output of said first delay line, a signal output and a control input, and a phase comparator for comparing in line-by-line fashion the phase of the color bursts of the reproduced video signal to the phase of a reference subcarrier signal and developing and applying to said control input an error voltage to vary the phase of the reproduced video signal in compensatory relation to the error voltage, said error voltage varying substantially linearly over a range including a first predetermined value when said color burst is in phase with said reference subcarrier and a second different predetermined value when said color burst is 180* out-of-phase with said reference subcarrier, apparatus for causing said tape system to lock to the correct color frame upon startup, said apparatus comprising, means operative to stabilize the position of the reproduced horizontal synchronizing pulses relative to said reference horizontal pulses to enable comparison of the phase of the color burst of the reproduced video signal relative to the reference subcarrier after initial random color frame lockup, voltage sensing means for sensing the value of said error voltage operative to determine the relative phase of the color burst of the reproduced video signal and said reference subcarrier, and means operative in response to displacement of the phase of the color burst of the reproduced video signal relative to said reference subcarrier by a predetermined angle to change the speed of said capstan by an amount sufficient to move said tape by an amount corresponding to one television frame.