Automatic fine tuning of receiver for digital television signals

A radio receiver for selectively receiving one of a plurality of television signals transmitted through respective television broadcast channels, at least some of which television signals are digital television signals transmitted by suppressed carrier vestigial sideband modulation with an unmodulated pilot carrier of the same frequency as the suppressed carrier in accordance with a data broadcast standard for terrestrial through-the-air television broadcasting in the United States of America, in which said data broadcast standard the pilot carriers of said digital television signals are at suppressed carrier frequencies substantially closer than 1.25 megahertz to limit frequencies of said television broadcast channels, said radio receiver comprising:

• circuitry for selecting said television signal currently being received, which circuitry includes a first detector for generating a first detector output signal;
• a first local oscillator included within said first detector, for supplying first local oscillations of adjustable frequency which frequency can be fine-tuned responsive to an electric fine-tuning signal;
• a first mixer included within said first detector for multiplicatively mixing said television signal currently being received with said first local oscillations to generate said first detector output signal;
• an intermediate-frequency amplifier chain for supplying an amplified response to said first detector output signal;
• frequency-selective filtering connected within said intermediate-frequency amplifier chain, which frequency-selective filtering provides selective response to said one of said digital television signals currently selected for reception, such that certain frequencies of said first detector output signal are amplified less than others in said amplified response to said first detector output signal supplied by said intermediate-frequency amplifier chain;
• circuitry for synchrodyning said amplified response supplied by said intermediate-frequency amplifier chain to baseband when said television signal currently being received is a digital television signal, thereby to generate a baseband symbol coding signal;
• symbol decoding circuitry for decoding said baseband symbol coding signal to reproduce a datastream, as transmitted in accordance with said data broadcast standard;
• a first bandpass filter providing selective response to the amplified response supplied by said intermediate-frequency amplifier chain for selecting said digital television signal pilot carrier as translated to intermediate frequency;
• and
• an automatic fine-tuning detector tuned for said digital television signal pilot carrier as translated to intermediate frequency, receptive at least at times of the selective response of said first bandpass filter as input signal thereto and supplying an output signal therefrom which is applied as said electric fine-tuning signal to said first local oscillator included within said first detector when said television signal currently being received is a digital television signal, thereby completing an automatic fine-tuning feedback loop.