oscillator phase noise

How to measure a crystal oscillator's phase noise, which is lower than the noise floor of our spectrum analyzer, is there any method?
Someone told me there was a kind of traditional method to measure the phase noise of such high Q oscillator. What's it? Is there any special instrument needed?

you need the phase noise measurement set up HP11729c + HP 8662A generator

or you can built one ( a very clean genarator + mixer + amplifier +filter)

Measure the phase noise of one of the higher harmonics (where the phase noise will be above that of the SA) of the signal. Then you can calculate the phase noise of the original signal according to which harmonic you used for your measurement. You may need to use quite a high Nth harmonic to obtain enough increase in phase noise for the SA to measure, but this method works well.

Go to this article:
"Theory and Practical Considerations for Measuring Phase Noise Better Than –165
dBc/Hz"
A simple registration is required.

http://www.mwjournal.com/getblob.asp...=0410mwj36.pdf