Understanding Phase Noise and Jitter

I'm sure all you experienced RF and Electrical engineers know how important Phase Noise and Jitter are. Phase noise can also get very confusing. Especially in RF and Oscillator applications. What are some good sources that you all recommend for getting an easy, basic understanding of phase noise and/or jitter?

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What other sources do you recommend? This way we can help out all those who are somewhat new to this important topic.

Thanks!
Rob