Erik, pls see attached application note for phase noise measurements. Page 31-32 describe the method you are trying to perform. Are you adjusting either signal to insure quadrature? The ADF4351 has the capability for adjusting the output phase, not sure if enough range is available to insure quadrature?
www.keysight.com/upload/cmc_upload/All/PhaseNoise_webcast19Jul12.pdf
Thanks!
On June 2, 2019, at 4:37 PM, erik@... wrote:
I'm using a 10MHz reference clock from the onboard xco. All settings can be seen in the screen grab of th ADF4351 tool in my first post. I tried with the doubler but that did not make a big difference. I also used the OCXO as reference as it has much better close in phase noise (below 1kHz) but no difference in noise above 10kHz
The ADF4351 module is the "green" ebay module. I also tested the black ebay module with 25 MHz onboard XCO reference, it has more spurs but comparable phase noise.
All modules have an ultra low ESR capacitor on the 3.3 regulator output
