Nyquist - overcoming the limitations

In digital signal analysis it is not possible by normal methods to retrieve components of frequency in excess of half the sampling frequency, generally referred to as the Nyquist frequency. Any frequency components that exist in excess of this value will give errors in their frequency determination because they will appear as false or 'aliased' signals. A new technique has been developed to unambiguously retrieve signals many thousands times greater than this hitherto stated limitation. A feature of the system is its ability to sample at low frequency and, without further sampling, be capable of unambiguously determining frequency components far in excess of the initial low-frequency sampling rates. Although the approach has its origins in the area of machinery condition monitoring it has applications in numerous other fields, such as lowering the bandwidth of frequency spectra within communication systems. The technique can also be used in reverse to synthesis high-frequency signals from transmitted lower frequencies. (C) 2004 Elsevier Ltd. All rights reserved.