What is the cause of the message "Measurement within 2 dB of Noise Floor" in my 2715 and 2714 CATV Spectrum Analyzer measurements?
The analyzer has its' own internal noise floor. If your cable TV system noise is less than the analyzer, then the accuracy of the measurement is in question for such measurements as Carrier-to-Noise. Your actual Carrier-to-Noise is better than reported, but it is unable to determine how much better. This is usually caused by making measurements in the headend where the signals have not gone through any amplifiers, which contribute noise. In the field, after several amps, this is not an issue. One temporary improvement that can be made in your 2715 or 2714 is to change the mixer input level in the Input Menu to -20 dBm instead of the default of -30 dBm. This improves noise performance of the analyzer, at the expense of worsening the distortion products generated by strong signals in the analyzer. Be sure to change this back to -30 dBm for measurements involving distortion, such as CTB and CSO. At power-up your analyzer will revert to the auto mixer level of -30 dBm unless a User-Defined Power-Up is saved with these settings.
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