Marco,

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Our calibration constants are really similar, which thickens the mystery.

With these results, we will have no choice but to measure at different locations and compare our measurements.

Let's take 2 easy points, AUX IF OUTPUT and AUX VIDEO OUTPUT on the rear panel.

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There should be no problem with that, but check if AMP CORR is OFF.

CAL

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AMP CORR

AMP CORR OFF

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- PRESET

- Put the 300 MHz REF on the 8591E connector

- SPAN 1 MHz

- ZERO SPAN

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The measurement on another Spectrum (or tinySA) at 21.4MHz on the AUX IF OUTPUT connector gives me about -51dBm, with a voltmeter on the AUX VIDEO OUTPUT output I have about - 300mV.

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If these two tests are OK, then we will have to measure near the ADC. I will wait for your results.

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Here comparison between the calibration’s constants.

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Test AUX IF and VIDEO output