[time-nuts] AN/URQ13 reference AT cut crystal?

[Bob kb8tq]

Hi

SC cut:

1534592 <https://ieeexplore.ieee.org/document/1534592>

First really talked about in the early 1980’s and at that point an HP oddity. 
At least in terms of actually being used in any sort of production product. 
There are quite literally many hundreds of “known” crystal cuts that *could* 
be used in an OCXO. Dig enough and the papers for this or that cut go back to 
something that came before. Eventually you get to the 1920’s. 

Based on knowing a number of the FE folks and having worked with some
of them, they had no interest in / role in the SC in the 1970’s. It takes a *lot*
of work to move a crystal cut from “known” to “production ready”. None of 
it is very exciting, but those 100’s of man-years do have to be put in. 

As an OCXO crystal, an SC with a turn at 40C would be a pretty terrible 
choice, even if you *could* stabilize the the oven(s). An AT would be a much
better way to go. 

Bob


> On Feb 17, 2021, at 9:38 AM, paul swed <paulswedb at gmail.com> wrote:
> 
> Bob
> I thought SC's were around a long time. (Not that I doubt you on that) This
> thing should be the 1970s vintage from the one bit I have found on it.
> Magnus always appreciate your comments. As I heat it up from room
> temperature what exactly would I look for? Sort of the
> temperature/frequency behaviors I see in various charts?
> When cold the units sit 4Hz high. and when warm its currently .119 Hz high.
> It used to go below by .6 Hz. Not sure what has changed.
> Regards
> Paul.
> 
> On Wed, Feb 17, 2021 at 9:31 AM Bob kb8tq <kb8tq at n1k.org> wrote:
> 
>> Hi
>> 
>> If it was made before 1981 it pretty much certainly is *not* an SC. That’s
>> not to say it is an AT. A lot of crystal cuts got used in OCXO’s over the
>> years.
>> 
>> My guess, it broke, somebody took it apart and threw away the defective
>> crystal. It was replaced with a random unit from the junk box and the ovens
>> were (effectively) turned off.
>> 
>> Bob
>> 
>>> On Feb 16, 2021, at 8:18 PM, paul swed <paulswedb at gmail.com> wrote:
>>> 
>>> After a bit of research I am wondering if this odd unit was actually an
>>> attempt at a AT cut crystal reference. The temperatures seem to line up.
>>> Its certainly an alpha or less product.
>>> It was stable at 43 F.
>>> Was thinking about disconnecting the oven and bringing the leads out to
>>> manually control the temp. With a quality external temp meter. Then see
>> as
>>> the temperature is adjusted, does it follow an AT cut curve.
>>> As someone on the thread said "it maybe working as intended".
>>> Regards
>>> Paul
>>> WB8TSL
>>> 
>>> On Tue, Feb 16, 2021 at 6:17 PM paul swed <paulswedb at gmail.com> wrote:
>>> 
>>>> Hello to the group still working and decoding the AN/URQ-13 reference
>>>> oscillator. Bob had mentioned that the crystal should be at 85 C and
>> thats
>>>> right for a SC cut crystal. Would there be any reason that this
>> oscillator
>>>> is perhaps a AT cut crystal thats in the 30 C range. Just odd that the
>>>> front meter reads in the normal temperature range and the real
>>>> measurement is 40C. Makes no sense but they build AT cut crystals for
>> some
>>>> reason.
>>>> Ehat about the smaller ovens like Piezo's. Pretty sure I can find many
>>>> details on the Morion oscillators like the MV200.
>>>> 
>>>> Other bits of details.
>>>> There are 2 discreet regulators that simply produce most likely a low
>>>> noise +/-8.5V. The Oven heaters seem to run on +15V and the divider
>> analog
>>>> circuits need 13V min to work. But not 15V. That seems to cause some
>>>> distortion.
>>>> The other circuit on the board attached to the oscillator is a buffer
>> amp.
>>>> It does have several meter resistors on it also.
>>>> 
>>>> Regards
>>>> Paul
>>>> 
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