[time-nuts] HP10544A Confusion

Jim Flanagan jflan at tampabay.rr.com
Fri May 29 13:47:57 UTC 2009


Hi..
I need help understanding a few things in regards to my 10544A oscillator.

I was given an osc about 5 years ago that did not have the oven 
controller.  The
owner at that time had built his own version which did not work well.  I 
completely
removed everything he had done and duplicated the original oven using the
osc schematics that are available.  At that point the osc went on the 
shelf until
a couple of weeks ago.  I decided to go ahead and calibrate the oven 
temperature
in order to select the correct resistor to set the temp at the turning 
point.

Here is my confusion:
I understand that the 10544 oscillators used AT cut crystals, which 
means that
after warmup, I need to tweak the temp for a freq MIN.  Whereas, for an SC
cut xtal osc we would be looking for a freq MAX.  For both xtal cuts the 
turning
point is typically set for somewhere in the 75 - 85 C range.  I see where my
10544 osc is sitting about 1.5KHz LOW at room temp and then increases
in freq at warmup (OVEN temp rising).  I thought that at room temp the
freq (for AT osc) would be HIGH and decrease in freq as the oven warms.
After a full warmup, I would then adjust the temp slowly, watching the 
freq for
a min, at which time, as the oven is made hotter, the freq would then 
start in the
opposite direction(positive).

In my mind, my osc seems to act as though it is using an SC cut crystal...
Is my thinking all wrong here?

I've been studying he classic df/f vs Temp curves and my osc appears to be
opposite of the curves, assuming my osc does use an AT xtal.

I would appreciate someone setting me straight in regards to this..
Thanks
Jim
jflan at tampabay.rr.com







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