| 摘要 |
In a receiver subject to SECAM signal reception, an FM detector responsive to the received signals has its center frequency tuning switched between one SECAM subcarrier center frequency and the other SECAM subcarrier center frequency. Control of the switching, in response to line rate, burst interval pulses and to half line rate waves from a triggered flip-flop, is such that tuning is different in image portions of successive line intervals, but the same in lead-in burst portions of successive line intervals. A first sampler effects sampling of the detector output only during alternate burst occurrences, while a second sampler effects sampling of the detector output during the intervening burst occurrences. Sampler outputs are supplied to a comparator which provides an output suitable for controlling disabling/enabling of flip-flop to establish correct phasing of the switching of the detector tuning. Where receiver is a dual standard receiver also subject to PAL signal reception, another output is derived from the comparator for control of the switching of the receiver between PAL-reception SECAM-reception operating modes.
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