| 摘要 |
The invention is intended to lock quadrature-amplitude modulation receivers for e.g. 16-QAM via a phase-locked loop back onto the reference carrier phase in the event of an incorrectly recovered carrier phase, with no need for differential coding nor a different transmission-end procedure to mark the reference phase. For this purpose, a pulse generator 5 is provided according to the invention which is started up by an alarm signal which is derived from the synchronisation failure of the data receiver 6 and whose pulse voltage is superimposed on the phase-lock voltage at the input of the voltage-controlled oscillator 2 in such a way that locking onto a different carrier phase condition of the voltage-controlled oscillator, which repeats itself until the alarm signal subsides, i.e. until the provided reference carrier phase is attained, shuts off the pulse generator 5. The pulse generator is preferably designed as an astable multivibrator 51, 52, whose pulse repetition frequency f = 1/(2RC.In3) is selected by corresponding dimensioning of its frequency-defining components 53, 54 in such a way that it becomes shorter than the response time of the data receiver 6 (Fig. 1). <IMAGE>
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