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

[Bob kb8tq]

Hi

> On Feb 17, 2021, at 2:10 PM, Tim Shoppa <tshoppa at gmail.com> wrote:
> 
> Magnus, were they trying to use the SC-cut crystal itself as a calorimeter,
> or something else?
> 
> if using a crystal as a calorimeter (essentially self-temperature probe) to
> detect axions, they do not want the crystal cut for stability at operating
> temperature?
> 
> You want to operate the crystal where it has the steepest possible
> temperature slope. I know dang little about the cuts and how they behave at
> cryogenic temperatures.
> 
> Of course vast quantities of crystals are used in particle physics but not
> as oscillators :-). I remember literature from back in the 60's there was
> some interest in crystals used as oscillator calorimeters but that's a
> pretty obscure corner of calorimetry today if anyone is still trying it.
> 
> We've had threads in the past on time-nuts about hysteresis in HP's
> crystal-based temperature probes. I guess in an axion calorimeter the
> hysteresis limits lower limit of detection.

…… and there are whole families of crystal cuts that have been optimized
for use as thermometers. There is no need to compromise on something
like an AT or SC if you are after temperature. There are lots of different 
cuts to pick between. 

You *do* run into the same issues as with OCXO crystals. The number of
cuts “known” is much larger than the number that are “production ready” ….


Bob


> 
> Tim N3QE
> 
> On Wed, Feb 17, 2021 at 1:04 PM Magnus Danielson <magnus at rubidium.se> wrote:
> 
>> Hi Paul,
>> 
>> On 2021-02-17 15:38, paul swed 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.
>> Research-wise, you come back to about 1974 it seems. Production seems to
>> start at about 1981.
>>> Magnus always appreciate your comments.
>> Uhm, I did not know that my appreciation for someones comments was used
>> as a hallmark for quality. I sit here in amazement of what just happen.
>> Bob has delivered insight from so many decades in the industry, and that
>> insight shows of in quality of posts, that is always appreciated.
>>> 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.
>> 
>> So, as you heat up from 20 C to 85 C the frequency shift. Depending on
>> cut, the start offset (cold frequency - nominal frequency) have
>> different sign and size, depending on cut. It's fairly easy to spot
>> different cuts that way we concluded.
>> 
>> You can dig up frequency error vs. temperature graphs for various cuts.
>> The AT-cut one is well spread third degree shape going up to a
>> saddle-point, going down to a saddle-point and then going up again.
>> Minimum sensitivity to temperature happens on those saddle-points.
>> 
>> I remembered a setup where someone used SC-cut oscillators in cryogenic
>> temperature setup to detect axions. He noted that they where fighting
>> temperature variations to the oscillators. I simply asked if the SC-cut
>> crystals had been cut for that temperature, and apparently not. Well,
>> there is a basic magic to the stability, and if you do not respect that
>> magic, do not expect the result to be so spectacular either. That said
>> from someone who have yet to design a single crystal oscillator beyond
>> following standard datasheet setup.
>> 
>> The Gerber & Ballato "Precision Frequency Control" books is a good read.
>> Chapter 12 by Sam Stein I know exists as separate PDF, maybe other parts
>> too. It has tabulated coefficients for AT, BT, IT and SC cuts cubic
>> temperature dependence.
>> 
>> Cheers,
>> Magnus
>> 
>> 
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