Analysis of Synchronizing Systems for Dot-Interlaced Color Television

A mathematical analysis is made of two synchronizing systems which might be used in "dot" color television to synchronize the dotting or sampling frequency in the receiver. Synchronizing information is transmitted in bursts of carrier cohered in phase of approximately 3 Mc during line fly-back time. The two systems analyzed are (1) a simple high-Q resonant filter and (2) an oscillator with automatic frequency control (afc). In order to maintain sufficient phase accuracy in the sampling frequency, crystal control at the transmitter is necessary. Since the variations of the frequency response of a particular crystal filter with time may be made essentially negligible, the problem resolves itself into calculating the parameters of the synchronizing system to keep below an acceptable value the random phase error due to noise together with the phase error caused by variations in frequency (static phase error) from crystal to crystal. Rather than attempt to minimize the sum of the random and static phase errors, the two have been dealt with separately because of their different character. A fundamental parameter in the calculations is the power carrier-to-noise ratio in the intermediate frequency, the carrier being measured at the sync tips. Calculations are made for values of this ratio of 1, 3, 5, this being considered the critical range. Results of the calculation show that when the phase error due to noise alone is fixed, the simple resonant filter and the afc with single time constant suffer the same static phase error.