Noise-reduction sampling system
First Claim
1. Receiving apparatus for separating a selected periodic wave from a plurality of waves occupying a frequency band which has a Nyquist frequency less than the frequency of zero crossings of said selected periodic wave, without band-stop filter means in the transmission path of said plurality of waves, which comprises:
- selection means which selects the carrier of said selected periodic wave and substantially eliminates other waves, andfrequency changing, phase shifting and pulse generating means which generates a sequence of gating pulses from said carrier occurring at instants of zero crossings of said selected periodic wave at a frequency greater than the Nyquist frequency of said frequency band, andgating means which receives said plurality of waves and is opened by said gating pulses to produce a sequence samples of said plurality of waves less said selected periodic wave, andfilter means which receives said sequence of samples, reconstructs from them said plurality of waves less said selected periodic wave, passes said frequency band and attenuates frequencies outside said frequency band.
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Abstract
This invention provides means and method of eliminating a selected wave from a frequency band containing a plurality of waves, by sampling the plurality of waves at a rate greater than the nyquist rate for the frequency band in herz, at instants at which the selected wave has zero amplitude, and integrating the sequence of samples so obtained to produce a replica of the plurality of waves less the selected wave.
The plurality of waves less the selected wave may be subtracted from the plurality of waves, after adjustment of relative amplitude and delay, so that the selected wave is obtained substantially free of other waves of the plurality of waves.
Thus a selected undesired wave, with a maximum period between successive instants of zero amplitude of less than the nyquist interval for the frequency band, may be substantially eliminated without affecting other waves; a selected desired wave, with a maximum period between successive instants of zero amplitude of one-half the period of the bandwidth of the frequency band, may be recovered substantially free from noise.
108 Citations
3 Claims
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1. Receiving apparatus for separating a selected periodic wave from a plurality of waves occupying a frequency band which has a Nyquist frequency less than the frequency of zero crossings of said selected periodic wave, without band-stop filter means in the transmission path of said plurality of waves, which comprises:
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selection means which selects the carrier of said selected periodic wave and substantially eliminates other waves, and frequency changing, phase shifting and pulse generating means which generates a sequence of gating pulses from said carrier occurring at instants of zero crossings of said selected periodic wave at a frequency greater than the Nyquist frequency of said frequency band, and gating means which receives said plurality of waves and is opened by said gating pulses to produce a sequence samples of said plurality of waves less said selected periodic wave, and filter means which receives said sequence of samples, reconstructs from them said plurality of waves less said selected periodic wave, passes said frequency band and attenuates frequencies outside said frequency band. - View Dependent Claims (2, 3)
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Specification