| 摘要 |
The present invention is used to cancel a narrow band noise of know frequency, such as 60 Hz noise generated by powerlines, in electromagnetic receiving equipment. A cancelling antenna is wrapped around the sensing antenna of the electromagnetic receiver equipment. The cancelling antenna is provided with an alternating current signal of the same frequency as the ambient powerline noise. The cancelling antenna produces an electromagnetic field that is 180 degrees out of phase and of equal amplitude to the ambient powerline noise, as measured by the sensing antenna. The alternating current is produced by a noise antenna, a phase-locked loop and an amplifier. The noise antenna receives the ambient powerline noise, the phase-locked loop locks onto and tracks the frequency of the noise, and the amplifier provides the necessary amplification.
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