An alternative symbol timing recovery circuit involves 'squaring' the
received filtered data stream, which yields a signal with a strong discrete frequency
component at the symbol timing frequency. Extracting this signal with a narrow tuned
filter or a phase locked loop gives the required symbol
clock. This system works well for a = 1.0, but will not
produce a discrete spectral line for small values of a.
Yet a
third method of symbol timing recovery is the early-late
gate method. This technique is described in connection with amplitude shift keying in Chapter 5.
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