HP 8591C, User Manual, Page: 260 / 373

Carrier-to-Noise Ratio Test Description
The result of the carrier-to-noise measurement is the ratio of the peak visual
carrier level (modulated or unmodulated) to the noise measured in one of the
manners described below. This ratio is normalized to a 4 MHz noise-power
bandwidth.
There are three methods of measuring carrier-to-noise:
1. In-between channels.
2. Disable modulation and measure over FCC range.
3. Non-interfering (using Option 107) and measure over FCC range.
1. In-between channels
In the first method, the peak carrier level is measured first, then it
continuously updates and reports the carrier-to-noise ratio for the marker
position. The marker can be moved as desired and the result is updated to
reflect the most current test result. At the end of each sweep, the marker
does a local minimum search as well as a local trace average.
Before executing the test, the analyzer initially measures the total power of
the entire cable system. This is done to set the attenuator to avoid overload
of the input mixer and noise floor lift due to internally generated distortion.
The analyzer then measures its own noise figure and uses this for calculating
the final carrier-to-noise value.
The analyzer input attenuation is set to both prevent input mixer
compression and minimize the noise level of the analyzer.
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