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
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