Here is the CH1 ADC input signal analyzed with a FFT for both 50MHz and 2.099GHz, both with cable connecting CH0 and CH1 (thru) and without any connection (isolation)
The phase noise of the SI5351 is visible in the 50MHz thru graph.
Dynamic range for 50MHz is 64dB due to leakage.
The signal level for 2.1GHz is 40dB down due to being the result of a 7/9 harmonic mixing.
The "leakage" for 2.1GHz is 10dB up compared to 50MHz
Net result is a loss of 50dB dynamic range leaving 14dB at 2.1GHz
