Re: [time-nuts] Improving the stability of crystal oscillators
In a message dated 10/11/2007 09:12:44 Pacific Daylight Time,
richard@karlquist.com writes:
Your last statement is not generally true. The block cannot be well
insulated because of the thermal overhead of the oven circuitry (the
heat has to escape). I explained in my 1997 FCS paper how to achieve
the isothermal condition, which is achieved by symmetry rather than
high amounts of insulation. The E1938A oven works quite well if the
insulation is omitted or replaced by poor insulation, except that it
consumes more power.
Rick Karlquist N6RK
Hi Rick,
thanks for the pointers to the E1938A oven quality.
Today there are some interesting new technologies which allow small double,
or even tripple (not sure if that makes sense) ovens to be built. Vectron for
example just had a lead-article in RFDesign magazine introducing their
newest evacuated OCXO's.
http://rfdesign.com/vlf_to_uhf/time_and_frequency/709RFDF1.pdf
(http://rfdesign.com/vlf_to_uhf/time_and_frequency/709RFDF1.pdf)
They claim stabilities on the order of 2E-07 over a very wide temp range of
-40 to +85C in a DIP14 can.
The 1/2 size DIP8 can is supposed to be available end of the year with
similar performance.
Those small cans and wide operating ranges should make it possible to build
a nice small and inexpensive oven. If one can get a true thermal gain of
1000+, then that would theoretically mean stabilities approaching 2E-010 over
temperature. That's 1.6E-012 per degree Celcius.
bye,
Said
************************************** See what's new at http://www.aol.com
At HP, in the 90's, we did a lot of brainstorming about vacuum ovens.
This never seemed to make sense to us. If you actually
achieve high amounts of thermal resistance, then you can't
get the heat out of the oven. And if you don't, why bother
with a vacuum. Also, a vacuum only helps if you do everything
else you need to do to make a true Dewar (thermos bottle), like
having mirrored surfaces, etc. Finally, having a vacuum means
that nothing that outgasses can be used in the oscillator.
Maybe Vectron has figured out something we didn't think of or
has sufficiently difference constraints that a vacuum makes
sense for them.
Rick Karlquist N6RK
SAIDJACK@aol.com wrote:
Today there are some interesting new technologies which allow small
double,
or even tripple (not sure if that makes sense) ovens to be built. Vectron
for
example just had a lead-article in RFDesign magazine introducing their
newest evacuated OCXO's.
_http://rfdesign.com/vlf_to_uhf/time_and_frequency/709RFDF1.pdf_
(http://rfdesign.com/vlf_to_uhf/time_and_frequency/709RFDF1.pdf)
They claim stabilities on the order of 2E-07 over a very wide temp range
of
-40 to +85C in a DIP14 can.
The 1/2 size DIP8 can is supposed to be available end of the year with
similar performance.
Those small cans and wide operating ranges should make it possible to
build
a nice small and inexpensive oven. If one can get a true thermal gain of
1000+, then that would theoretically mean stabilities approaching 2E-010
over
temperature. That's 1.6E-012 per degree Celcius.
bye,
Said
SAIDJACK@aol.com wrote:
Hi Rick,
thanks for the pointers to the E1938A oven quality.
Today there are some interesting new technologies which allow small double,
or even tripple (not sure if that makes sense) ovens to be built. Vectron for
example just had a lead-article in RFDesign magazine introducing their
newest evacuated OCXO's.
_http://rfdesign.com/vlf_to_uhf/time_and_frequency/709RFDF1.pdf_
(http://rfdesign.com/vlf_to_uhf/time_and_frequency/709RFDF1.pdf)
They claim stabilities on the order of 2E-07 over a very wide temp range of
-40 to +85C in a DIP14 can.
The 1/2 size DIP8 can is supposed to be available end of the year with
similar performance.
Those small cans and wide operating ranges should make it possible to build
a nice small and inexpensive oven. If one can get a true thermal gain of
1000+, then that would theoretically mean stabilities approaching 2E-010 over
temperature. That's 1.6E-012 per degree Celcius.
bye,
Said
Said
The lack of radiation shields and an isothermal block enclosing the
oscillator components within the vacuum will surely reduce the
performance somewhat.
Bruce