TELEVISION MODULATING CIRCUIT

PURPOSE:To synchronize the output frequency of a television modulator with a reference frequency by branching respectively the 1st local oscillation frequency and the 2nd local oscillation frequency and forming a frequency the same as that of an output carrier signal with a modulator other than a main modulator. CONSTITUTION:A frequency f1 of the 1st local oscillator 7 is branched into two; one is fed to a television IF modulator and also the other is fed to a modulator 42. A frequency f2 of the 2nd local oscillator 38 is branched also into two; one is fed to a VHF modulator 4 and the other modulates the frequency f1 of the 1st local oscillator in the modulator 42. A frequency of fv=f2-f1 is obtained at the modulator 42. The frequency fv is carrier frequency of a television signal tv at an output terminal 6. A carrier extracting circuit 39 extracts the fv component. The frequency of the fv component and that of a reference frequency rf are compared by a frequency converter 41 so as to control the frequency of the 2nd local oscillator 38.