[time-nuts] Close in phase noise of microwave VCOs

Jim Lux jimlux at earthlink.net
Thu Jun 18 15:09:12 EDT 2015

On 6/18/15 3:46 AM, Bob Camp wrote:
> Hi
> Be careful when you do find the data.
> When you go very close in on something like a VCO, you get much higher phase noise
> than we normally worry about. Some of the “assumptions” that underly the measurements
> are no longer true. Small angle of modulation is one, but there are a few others.

yeah that's a big one.. There's a slide in a recent Keysight/Agilent 
presentation on phase noise measurement that has a line on it at, I 
think, 30dB/decade going through -30dBc at 1Hz or something as the 
threshold where small angle approximation is no longer valid.

  A simple
> “plug it in and read it” may not give you valid information without some corrections.  Coming
> up with a supply that’s good enough (at 1 Hz) would be a major challenge ...

Well, it's not like we're looking for 1E-10 ADEV in this sort of 

Mostly, it's a "what should you expect".. and also the whole "we all 
know gunn oscillators are noisy, but how noisy, really"

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