In-service measurement of composite triple beats in a cable tele

Details In-service measurement of composite triple beats in a cable tele In-service measurement of composite triple beats in a cable tele

1995-05-30

1997-04-01

Peng, John K.

Television

Monitoring, testing, or measuring

Transmission path testing

348192, H04N 1700, H04N 1702

Patent

active

056171374

ABSTRACT:
An in-service composite triple beats (CTB) measurement system for a cable television (CATV) system isolates and measures weak composite triple beat components in the presence of a visual carrier modulated with program material for selected channels of the CATV system. Each channel is demodulated and digitized in a frequency bandwidth about the visual carrier for the channel (the CTB frequency range). The digitized video is sampled during the vertical interval, and corresponding samples from consecutive frames are differenced, squared and accumulated to produce a CTB value, which may be scaled and corrected for noise. Noise correction is achieved by performing the same measurement, but digitizing in a frequency bandwidth offset from the CTB frequency range. The difference between the two measurements provides a corrected CTB value. For further accuracy the automatic gain control of the demodulator may be enabled only during the vertical interval, and the frequency control of a phase locked loop that produces the clock for the digitization of the video signal may be turned off during the vertical interval. Finally the amplitude of the sync tips of the demodulated video signal may be minimized prior to digitization.

REFERENCES:
patent: 5073822 (1991-12-01), Gumm et al.
patent: 5323239 (1994-06-01), Ward et al.
patent: 5493209 (1996-02-01), Gumm et al.
"NCTA Recommended Practices for Measurements on Cable Television Systems" Second Edition, International Standard Book No. 0-940272-17-2 (pp. 4-5).

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