Hi,

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To make a first comparison, here is the output of my 8753ES at 1GHz, CW mode, 0dBm output, Trigger HOLD, measured on a Spectrum.

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If you have a similar image, the PLL A11 would be correct.

You do not have an UNLOCK message, this means that you have enough signal to maintain synchronization.

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If the signal going to the sampler R was attenuated, the average during an S11 measurement would give an average signal offset from the reference (when nothing is connected to port #1).

But looking at your image, test S11, nothing connected to port #1, apart from the noise everything seems correct.

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Do a test from 30kHz to 250kHz, the A11 module is bypassed, if the problem persists, A11 is not the cause.

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Either the problem comes from A7, or it is further away like on the IF DIGITAL.

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Make measurements on the samplers separately, MEAS A, B and R. Do you have the noise problem on all samplers.

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I will wait for your answer, and I will be able to make comparative measurements on my VNA 8753ES.

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Yves

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