H - Electricity – 04 – N
Patent
H - Electricity
04
N
350/97
H04N 5/60 (2006.01)
Patent
CA 1318973
METHOD AND APPARATUS FOR DETECTING A DESIRED TELEVISION SIGNAL ABSTRACT OF THE DISCLOSURE A detector indicates the presence of a desired signal when both of at least two conditions occur. The first condition requires the presence of a selected frequency in an input signal and a second condition requires the amplitude of the input signal at the selected frequency to fall within a predetermined range. A third condition requires that one or both of the first and second conditions have a duration of at least a selected period of time. In one embodiment, the detector indicates the presence of a stereo audio signal in a television transmission program when (1) a pilot frequency (15.734 khz) is present in the composite baseband, (2) the signal amplitude at the pilot frequency corresponds to a fre- quency deviation of not more than 5.5 khz and not less than 4.5 khz from the 4.5 mhz carrier frequency, and (3) the two afore- mentioned conditions exist for a predetermined period of time, preferably about one millisecond. In another embodiment, the detector indicates the presence of a second audio program (SAP) in a television transmission program when (1) the SAP carrier fre- quency (78.67 khz) is present in the composite baseband, (2) the signal amplitude at the SAP carrier frequency corresponds to a deviation from the sound carrier signal of not more than 16.5 khz and not less than 13.5 khz, and (3) the aforementioned two con- ditions are present for a predetermined period of time, preferably about one millisecond.
593585
Fetherstonhaugh & Co.
Motoyama Tsutomu
Philips Electronics North America Corporation
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