| 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 th e actuation of an alarm (48) when the variation ex- ceeds a predetermined amount; and signals whose frequency components have be en 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 sig- nal channels, selectively amplifying or attenuating the signal in each chann el and combining the signals in each channel (67).
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