[time-nuts] Re: E1938A phase noise improvement

[Bob kb8tq]

Hi

There are not many single oven designs out there that achieve
the stability of the E1938. Of the designs I’m aware of, all use
a “correction signal” to get there. Double ovens are a totally 
different beast …..

Bob

> On Dec 26, 2021, at 12:14 PM, Attila Kinali <attila at kinali.ch> wrote:
> 
> Hoi Rick!
> 
> On Sun, 26 Dec 2021 08:36:06 -0800
> "Richard (Rick) Karlquist" <richard at karlquist.com> wrote:
> 
>> The E1938A has both an ALC loop (common in many oscillators) plus an AFC 
>> loop, which is exclusive to the patented bridge stabilized circuit.  I
>> am thinking that maybe the AFC circuit was causing the hump.  That
>> theory could be verified by disabling the AFC and seeing if the hump
>> goes away.  The AFC is not necessary just to make the oscillator play
>> for noise testing.
> 
> May I ask a heretic question? Does the AFC actually improve
> stability?
> 
> I looked at quite a few OCXO circuits (that are still in use)
> over the past years. Of them, the E1938 is the only one that
> tries to compensate changes within the oscillator at all
> (besides ALC). Yet there are many other oscillators that acheive 
> similar stability values as the E1938.
> 
> You hav written a nice description[1] of how the oscillator does
> work and why it should be better, but there are no comparisons
> of the ciruit with and without AFC. Or even a standard Pierce
> versus the Balanced Bridge. Which for me raises the question,
> whether the additional complexity is justified. Especially given
> that the bridge circuit halves the available Q and thus increases
> 1/f^2 and 1/f^3 noise.
> 
> 			Attila Kinali
> 
> [1] "A New Type of Balanced-Bridge Controlled Oscillator",
> by Richard Karlquist, 1999
> http://www.hpl.hp.com/techreports/1999/HPL-1999-6.pdf
> -- 
> The driving force behind research is the question: "Why?"
> There are things we don't understand and things we always 
> wonder about. And that's why we do research.
> 		-- Kobayashi Makoto
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