Setup and measure of phase noise using spectrum analyzer

Hello guys,

Could you, please, give me a suggestion about my setup to measure phase noise using direct spectrum measurement?
Oscillators are connected directly to spectrum analyzer in free-running operation.

I want to measure two circuits: (a) ring oscillator and (b) lc-tank circuit - shown in figure 1 and 2. The LC-tank circuit does not have tune voltage and it is not possible to change its capacitance.

1) We know that direct measurement is not the ideal way to measure in-close phase noise due to the frequency shift, but my LC-tank does not have tune voltage.

Does this setup work to properly measure PN for the lc-tank and ring oscillator?

I would say that it can work for lc-tank but not for the ring-oscillator. I'm not sure.

2) Phase noise is usually calculated using: Phase noise (f) = PSSB (f) - PS - 10 log (B) + C . where B is the resolution (RBW), PS = total carrier power and PSSB is 1 Hz one-side power density in offset frequency. Usually C is around 2.5 dB.

How can I estimate a more realistic value of C for my spectrum analyzer?
I dont know how to get this value.

Thank you very much for any comment.