[time-nuts] HP10544A Confusion

[Bruce Griffiths]

There was a design change between the issue of the 1972 and 1975 datasheets.
The 1975 and later datasheets state that the oscillaor circuit was
modified from the earlier version.

The latter oscillators had a 15dB lower phase noise floor.
The oscillator supply voltage specs also changed as did the oven voltage
specs.
It is likely that the later models used a BT crystal whereas the earlier
ones used an AT crystal.

Bruce

Jim Flanagan wrote:
> Jimmy -
> I found out the answer the question that I was asking you in
> my previous email.
>
> A fellow who is well versed in the HP oscillators (10544 and
> 10811) let me know that the 10544 oscillators used BOTH the
> AT crystals and the BT cut crystals.  This is why I was
> seeing what I was seeing.  Therefore I do need to tweak
> the temperature for a freq MAX.
>
> You may want to amend your website to point out that the
> HP10544A used BT cut crystals at some point.  All of the web
> references that I ran across pointed to the AT crystal
> as the only cut used during the lifespan of this oscillator.
> Take care-
> Jim
> -----------------------------------------------------
>
>
> 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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