What is the state of registers R0..R5 at power-up?
I have problem of RF-OUT glitch at power-up prior of micro-controller POR time allow the write into ADF4351 to setup rights operatives values.
The register values are unknown before you program them. You could hold CE low while programming the registers and then bring CE high when the registers are written.
Or possibly place filter after the RF output to filter the glitch.
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