| 摘要 |
<p>The method detects a periodic signal containing a sinusoidal carrier modulated with a rectangular wave. The modulated carrier frequency represents the information with a superimposed sinusoidal noise signal, having a time varying frequency within a predetermined window. The method involves detecting the frequency of the noise signal. The noisy signal is then filtered to determine the half spectrum of the noise signal. This is filtered to determine the main characteristic line in dependence on the frequency of the noise signal, and the presence or absence of a direction change in the modulated signal. An associated appts. includes a magnetic pick-up (2,3) and a detector circuit (4) to analyse the detected signal, using two band-pass filter groups. A switch, controlled by a noise frequency signal, feeds the periodic signal to one of the filter groups, depending whether the noise frequency is greater or less than that of the modulated carrier. A second switch, controlled by a direction change in the modulated signal, feeds the signal to the first or second filter of the second group. A comparator determines the filter output where the signal amplitude is greatest.</p> |
