[time-nuts] Calibration and temperature
Magnus Danielson
magnus at rubidium.dyndns.org
Sat Nov 29 12:40:40 UTC 2008
Lux, James P skrev:
>
>
> On 11/28/08 11:27 AM, "Bill Hawkins" <bill at iaxs.net> wrote:
>> Has any work been done on temperature compensation of quartz or other
>> oscillators to avoid the expense, space, and power of ovens? The
>> oscillating material must have a repeatable temperature curve, of
>> course.
> Look at MCXOs, a very clever technique using the different between third
> overtone and fundamental to measure the temperature of the rock.
The fundamental and third overtones have different temperature
dependencies. The difference is essentially linear, so by dividing the
third overtone down by three or tripping the base frequency and then
compare them in a mixer to get the beat frequency and count that,
adjustment to the frequency can be performed, often through a DDS
clocked at the third overtone.
The traditional suppression of major resonances becomes slightly
different in the oscillator core, since now both the fundamental and
third overtones is wanted. It is however not a big mystery.
You could use this temperature sensing technique to with an OCXO
solution to let the inner oven be sensed in the crystal. A combined
solution would both feed forward and feed backwards.
The MCXO and many others is very well presented in the big presentation
that John Vig has
(http://www.ieee-uffc.org/freqcontrol/tutorials/vig3/vig3.ppt). In
general, there is plentifull of good information to read at:
http://www.ieee-uffc.org/fcmain.asp?view=review#tutor
Reading through that and parts of the NIST T&F archive should elivate
your knowledge pretty fast and it is all for free. Just costs you the
time to read.
Cheers,
Magnus
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