sandman
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Thanks, David and Yawei for your inputs.
I thought I should mention the context of my question, just to put things into perspective.
I have an oscillator that runs at nearly 15GHz and has a -3dB bandwidth of about 30 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 very 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) , which at the moment has a fluctuation in it's central frequency to the tune of a say 1-5MHz. 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.
There's one thing though - the machine fails to track the oscillator signal even if I increase the error tolerance 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 10-15%.
Yawei, at present I'm trying two settings for the resolution bandwidth. In one case I allow the machine to set it's on RBW and in another I set it myself to be as large as possible, manually. In the first setting (automatic) I get an output which has steps (probably due to the changing RBW and the inability of the machine to track the signal peak) in the PN profile. In the second I get a smooth response, but I'm sure the measurement is accurate.
Any inputs are welcome !
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