[time-nuts] Re: Is SC the most stable cut for lowest phase noise?

[ghf at hoffmann-hochfrequenz.de]

Am 2022-06-08 21:53, schrieb Tom Van Baak:
> Would it be advantageous, then, to run a high-performance laboratory
> oscillator at its lower turnover point? Or at -78 C (CO2) or 77 K
> (liquid Nitrogen)?

I have no idea about the crystal itself. Maybe Bernd or the SC 
(SantaClara)
veterans can help?

When I measured the Q of the recovered SC crystal from that Morion 
MV89A,
there was not much of a difference in the wanted resonance between room
temperature and +89°C. I think I have published the data here a year 
ago.
My deep freezer in the basement can do -36°C, but the VNA is so heavy...

Infineon boasted that their SIGET transistors work nicely at a few 
Kelvin,
so it would probably not fail for semiconductor availability (BFP640 & 
friends).
OTOH, Ulrich Rohde wrote that the noise figure of the sustaining 
amplifier would
take a hit under large signal conditions, but I don't know hard numbers.
That would not disappear.

But then, in a Driscoll for example, you can give the 2 transistors 
enough
current so they run class A and do the little bit of limiting on the 
output side
with Schottkys. For the amplifier, that is not large signal.

That might be different for an amplifier in Lee-Hajimiri style.
This is Dirac pulse excitation at the peak of the cycle to avoid phase 
modulation,
that is optimized for mixing up 1/f noise.  :-)

Anyway, with a noise figure of the sustaining amplifier of a dB or even 
a few,
there is no game changer to be expected from cooling.

Whispering gallery saphire, anyone? I was at the precious stones museum
in Idar-Oberstein here in the 'hood and saw all these huge saphires.
I left with the head full of ideas...

Cheers, Gerhard