Signal Purity Considerations For Frequency Synthesized Headend Equipment (1984)
By David L. Kelma, General Instrument
As cable television system bandwidths increase and frequency plans proliferate, more manufacturers are turning to synthesized frequency agile headend channel converters. With this new approach using phased locked loops and dual conversion come spurious signals and noise sources not encountered before in crystal controlled channel converters.
Important characteristics of these headend converters including phase noise, spurious signals generated by the comparison frequency, and residual frequency and phase modulation, are evaluated for their subjective impact on the output signal to the cable. Data is presented which shows the correlation between subjective picture degradation and measured headend synthesize noise contribution.
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