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

Richard (Rick) Karlquist richard at karlquist.com
Sat Jun 20 20:35:54 UTC 2015

On 6/20/2015 6:25 AM, Jim Lux wrote:

> This makes a good case for the "30dB/decade very close in"

Somewhat had asked about "how" close in the 30 dB/decade is
good for.  There is a reference about this issue.  The
book Edson: Vacuum Tube Oscillators has what I believe is
the first published calculation of oscillator phase noise.
Way before Kurakowa and Leeson.  Edson has a formula that
gives the 3 dB bandwidth of the oscillator signal.  It's
not really a bright line.  This bandwidth is typically
a small fraction of a Hz for the oscillators Edson is
talking about.  However, for an unsophisticated 10 GHz
oscillator, it might amount to something that matters.

I think Edson also had a paper in Proc. IRE around 1950
that might have discussed this.

An interesting anecdote about Edson's book.  When I got
out of college I worked on RF oscillator design for
Boeing Electronic Products and learned about what was then
a very obscure topic called phase noise.  I was no expert,
but could at least say the right buzz words.  At the time,
the only book about synthesizers was Phaselock Techniques,
which I studied extensively.  It didn't have much on
phase noise.

In 1975, I interviewed for a job at another company
designing marine radios.  They wanted to replace crystals
with a synthesizer.  The hiring manager I interviewed with
was just about at the end of his rope because most
applicants couldn't even spell phase noise.  At some point,
I realized I had a lock on the job.  My new boss taught me all about
phase noise using Edson as a text book.


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