GB1482241A - Circuit for the automatic tuning of a receiver - Google Patents

Abstract

1482241 Automatic tuning circuit for a TV receiver INDESIT INDUSTRIA ELETTRODOMESTICI ITALIANA SpA 5 May 1975 [8 May 1974] 18814/75 Heading H3A A TV receiver capable of receiving a carrier frequency signal PV modulated with picture signals and at least one further signal PS modulated with sound signals, and containing a local oscillator 3, an IF amplifier 5 having the frequency response curve of Fig. 2, and a detector 10, 20, also incorporates an automatic tuning circuit comprising means 23 for generating a control signal dependent on the ratio between the amplitudes of respective signals representative of the amplitude of the detected PV signal and the amplitude of a detected signal of another frequency, the control signal being fed to oscillator 3 so that its frequency is adjusted to maintain the said detected amplitudes in a predetermined ratio. The second signal may be signal PS, or the colour subcarrier signal PC; it may also be an auxiliary signal injected into the received TV signal (e.g. of half the frequency of PC) and may be injected into alternate lines, the other lines being injected with the colour reference signal. Means 23 may be a differential amplifier. The signal representing the amplitude of PV may be derived from the AGC circuit 6, 10 of the IF amplifier 5. If the second signal is PC, then the signal representing its amplitude may be derived from a detector circuit 20 sensitive to the amplitude of the colour reference signal, or alternatively from the AGC circuit of the chrominance channel 9, 19-21, 25. Oscillator 3 may be a voltage controlled oscillator incorporating a varicap diode. The tuning circuit may be put out of action, when monochrome signals are being received, by means of a manually operated switch 24 or an electronic switch controlled by the colour suppressor circuit. The remainder of Fig. 1 shows a conventional TV receiver, with mixer 4, audio channel 7-15, sync separator 11, luminance channel 8 &c., deflection generators V, H, a decoder 22 producing B-Y, R-Y signals and a matrix 16 producing R, G, B signals.