| 摘要 |
Signals received (44) by an electronic article surveillance system are processed digitally (64, 65, 70, 72, 73, 76, 78, 82, 84) to ascertain the variation in magnitude of successive signals and to prevent the actuation of an alarm (48) when the variation exceeds a predetermined amount; and signals whose frequency components have been phase shifted from a filtering operation (62) are restored by passing them into a signal delay circuit, tapping the delay circuit at several points therealong into associated signal channels, selectively amplifying or attenuating the signal in each channel and combining the signals in each channel (67).
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