| 摘要 |
Method of selecting television signals, especially in a two-channel redundant link, characterised in that it consists, after detecting the synchronising pips indicating within each line in succession of the frame the presence of the video signal in each channel, in measuring sequentially in tempo with a clock the signal-to-background-noise ratio of each pip, in inverting this signal from one channel to the other and then in filtering it in order to eliminate the low-frequency or recurrent components, next in mutually subtracting the two signals in order to provide, in tempo with the pips, a resultant signal in which the noise component is centred on zero between two pulses, which are positive and negative respectively, dependent on the slight phase shifts between the two subtracted signals, the said pulses being blanked (suppressed) by a filtering circuit with dual monostable which recalibrates the synchronising pips and controls an analogue switch allowing the noise alone to survive and finally, depending on the result of the measurement, in switching the link to the channel for which the signal-to-noise ratio is highest. <IMAGE>
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