Hi all!

I have an oscillator that runs at nearly 8GHz and has a -3dB bandwidth of about 40 MHz. It's not a traditional LC or CMOS oscillator and which is why I'm trying to characterize it's phase noise. The carrier power is low (@ -40dBm) and is above the noise floor of the measurement setup by say 30 dB (which I agree is noisy!).

I'm using the direct measurement (method) to measure the PN profile of this free running oscillator (using a R&S FSU26 with a software PN add-on kit available from the same company). The oscillator at the moment has a carrier frequency drift, to the tune of a say 10-15MHz. I assume that because of this fluctuation the machine measures frequency noise and not just the intrinsic phase noise of my oscillator. I still don't understand this fully and it would be great if you or anyone would have some inputs or comments on this and what steps I would need to take to measure this noisy, very low Q, very low power oscillator.

Additionally, the machine fails to track the oscillator signal even if I increase the error tolerance (in frequency drift and signal peak power) to large percentages. So, I manually specify the level and frequency of the carrier for the PN measurement. I'm willing to live with some percentage of error in this measurement assuming it is - say, below 10%.

Any inputs are welcome. Thanks !