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An increase in the Displayed Average Noise Level is often the result of incorrect gain in the signal path. There may be an assembly with low gain that is compensated for by adding excessive gain elsewhere in the signal path. See the analyzer Service Guide for troubleshooting information.
If the Preamplifier On DANL fails and the DUT has Option 543, 544, or 550, with a preamplifier option of P03, P08, P13, or P26, and the instrument firmware is below A.10.51, then upgrade the DUT to the latest instrument firmware and repeat the test.