| 摘要 |
A test (600) system for characterizing the nature and the severity of the impairments affecting a radio frequency signal path (148) which may be an upstream or a downstream channel in a cable system. Testing is done by monitoring the output of an unused signal path (614) with a filter (608) and a totaling counter (612). The filter passes impairment energy from the signal path to the counter in a frequency band of interest, thereby increasing the count value on the counter. The bandpass filter limits the ability of impairments or signals from other frequency bands to increase the counter's count value. The counter's input threshold voltage level (404) is set to trigger on impairments that are sufficiently strong to cause data errors. The count value may be used to determine the time duration of an impairment by dividing the count accumulated in one second by the center frequency of the filter. An optional digital time trace acquisition unit (710), connected to the broadband signal path output (614), may be employed to capture time traces (734) to help identify the source and the nature of the impairment. The time traces can be stored, retrieved, and analyzed by conversion into the frequency domain, by digital filtering, by plotting as a histogram, and by plotting as a waterfall display.
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