I am doing phase noise measurement on a Giga Hz PLL.   The signal is probed from the pads which located between the VCO and Prescaler. Can I  directly feed this signal to with a serial capacitor?  The impedance at the probe pad is not 50ohms. Do I need a match network to get the signal out? Is the phase noise measured from the Spectrum analyzer changed if the VCO output signal power level changed due to the probe setup?

Any one can help me on these issues? Thanks.