A signal seeking tuning system of a television receiver includes a composite synchronization detector which generates a logic "0" when various parameters of the composite synchronization signal is correct and a logic "1" when they are incorrect as the local oscillator frequency is being decreased. After...http://www.google.com/patents/US4357632?utm_source=gb-gplus-sharePatent US4357632 - Search type tuning system with synchronization signal presence transition detector
