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Analysis of Spectral Component at Nyquist Frequencies During Receiver Start-Up Disclosure Number: IPCOM000064308D
Original Publication Date: 1985-Jun-01
Included in the Prior Art Database: 2005-Feb-18

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Godard, D [+details]


According to CCITT Recommendation V. 27, the synchronizing signal in 4,800 bits/sec. modems is composed of alternations between two signal elements, which produce two tones at Nyquist frequencies. This article describes two methods of analyzing separately the received tones at Nyquist frequencies. Referring to Fig. 1, upon reception of the synchronizing signal, the output signal from the Hilbert matched filter (HMF) is given by: (Image Omitted) Cartesian-to-polar coordinate conversion of the left hand terms in (5) and (6) provides the amplitude and phase of the tones at Nyquist frequencies. This is illustrated in Fig. 1. Fig. 2 illustrates a method of analyzing the received tones at Nyquist frequencies, which does not require any demodulation operation.