Brian Flynn GM8BJF
That is a new board to me as it has the microcotroller chip on it along with an OLED display.
Some of the earlier more basic boards used pretty ordinary voltage regulators and were quite Phase noisy.
I see this one uses a Linear Technology chip which I take to be a low noise voltage regulator so the PN performance is probably OK.
The "black ADF4351 boards" use a generic LM1117 regulator which could be improved on
If it is an issue you can add LF decoupling to the power rails on the board.
The ADF4351 is quite useful chip and can provide a reasonably clean signal. A 4 GHz signal generator for £25 cant be too bad!
I made myself a simple sig gen using one of the "black boards" and Cypress USB interface which can be made to work
with the AD demo software quite easily. I have had about a dozen of these sig gen boards from China and never had a problem with any of them.
They do what they say in the ads and are about a tenth of the price of the actual AD demo boards.