Dual time constant afc filter

Abstract From the Canadian patent

An AFC filter is described for use in a television receiver having a local oscillator and circuitry for developing an error signal which controls the frequency of the local oscillator. The filter receives the error signal and couples it to the local oscillator via two paths. The first path quickly couples the unfiltered error signal to the local oscillator for a brief interval to permit the latter to achieve rapid frequency lock. The second path filters the error signal to remove unwanted frequency components therefrom, couples the filtered error signal to the local oscillator after the latter has achieved frequency lock and renders the first path inoperative. Muting circuitry is included …