When to enable low spur mode of the ADF4351

For some time I have been fine tuning my spectrum analyzer. Did some improvements like replacing the cavity filter with a much narrower version so the 10.7MHz second IF no longer creates spurs.
And I have replace the Ceramic 30kHz resolution with a 6 pole crystal filter with 40kHz bandwidth but much better form factor.
The total looks now like this with shielding removed:




The phase noise picture overall looked ok apart from some annoying spurs between 30kHz and 100kHz and many small spurs above 200kHz:



After trying many things I switched on the low spur mode of ADF4351 first and second LO and that did make a difference:



Although the phase noise around 30kHz went up with 5dB most of the spurs there did disappear. Did not yet look into the spur at 150kHz
For the many spurs above 200kHz, these are caused by the PC and its USB peripherals as the unconnected Audio input has low noise floor but as soon as connected to the Spectrum Analyzer the noise goes up 20dB.
One small step completed, many to go, the journey is the goal.

Measuring phase noise of a single ADF4351 module

Till now I always measured phase noise by using multiple ADF4351 modules. To understand the impact of loop current and loop filter changes it would be better if it would be possible to measure the phase noise of a single  ADF4351 module. The maximum XCO I have is at 10MHz. Because of the output divider in the ADF4351 the lowest multiple at 50MHz (DIV64) has too low phase noise to measure as can be seen in the datasheet



Instead I went for a setup at 430 MHz using a divider of 8 (DIV8) resulting in 20dB more phase noise:



The 43nd harmonic of the 10MHz signal is filtered out and amplified and send as LO signal to as passive DBD mixer. The output of the mixer goes to a PC using a good microphone input.
Without the LO signal connected to the mixer, ARTA show the noise floor of the microphone input.



Good enough for this measurement.
With the LO connected the noise floor goes up which will limit the noise measurement possibilities




With the ADF4351 connected and using these settings:



I get the following measurement in ARTA using a 65536 bin FFT with FS at 192kHz (3 Hz per bin) so the measurement is 5dB above a /Hz measurement. Output signal of the ADF4351 is at +5dB but the noise is measured relative to the main output signal.



The 0dB peak at 200Hz can be moved around (even to 0 Hz) by tuning the OCXO. Phase noise at 10kHz seems to be at -100dB (compensating -5dB for the 3Hz FFT bins) which is about consistent with a simulation using ADIsimPLL using a loop filter of 15kHz



The phase noise however extends to much higher frequencies before it starts to decrease. Decreasing the charge pump current substantially leads to a noise increase at 10kHz as can be seen below



This looks more like the loop filter has a 60kHz bandwidth but according to ADIsimPLL the 10kHz noise should be 10dB lower with a 60kHz loop filter
So now my questions before I start to exchange loop filter 0603 SMD components or low noise 3.3V regulators:
- Is this an appropriate method for measuring the phase noise of a single ADF4351 using only simple equipment?
- How to improve the measurement?
- Is the loop filter bandwidth 60kHz or is it 10kHz and is something else pushing the 60kHz noise up such as a noisy regulator?