[time-nuts] State of the art of crystal oscillator measurements

Richard (Rick) Karlquist richard at karlquist.com
Thu Aug 11 13:39:50 EDT 2016

On 8/11/2016 5:01 AM, Mike Feher wrote:

> This may be a naive question, but, how can you achieve results that are so
> close to, and sometimes at further out are below kT? Thanks & 73 - Mike

> Mike B. Feher, EOZ Inc.

kT per see is not the relevant parameter.  It is the
ratio between kT and signal level that determines the
limit on phase noise.  Also, when you extract an
oscillator signal through the resonator, then at offsets
from the carrier, the resonator filters out noise and
the output noise can be way below kT.  Ulrich first
published on this in 1977.  Earliest reference I know of.
I actually remember reading it in 1977.

The old HP608 signal generator routinely produced far
out phase noise floor well below kT.  AFAIK, for this
particular spec, it better than any other signal generator
ever built.  What's the secret?  It has a tracking
POST-selector filter that follows the oscillator when
you turn the mechanical tuning knob.  There is a little
tracking adjustment knob to peak it.  Not really magic.


More information about the time-nuts mailing list