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

[Bob kb8tq]

Hi

> On Feb 17, 2021, at 6:31 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
> 
> 
> kb8tq at n1k.org said:
>> …… 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.  
> 
> How many degrees of freedom are there if I want to make a crystal?  What 
> fraction of the space has been explored?

Axis orientation is defined by the crystallography of the materiel. That’s been 
pretty well understood for a long time

https://www.nature.com/articles/154157b0 <https://www.nature.com/articles/154157b0>

> 
> Rotation in 3D has 3 degrees of freedom, but we are making a plane so I think 
> we get one back.
> 
> How accurately does a the crystal have to be oriented?  If I'm doing a brute 
> force search, how close together would I have to make test samples in order to 
> not jump over something interesting?

Fractions of a degree on each axis


> 
> 
> If I pick a type of cut, say AT, does the shape (round, rectangular) effect 
> the temperature profile?

Yes. It also impacts if it works at all. Get the shape wrong for this or that
orientation and you get nothing. 

You also have a number of vibrational modes. Each of them is excited by
different electrode configurations and mounting structures. 

>  If it's rectangular, that may add another degree of 
> freedom.

Turning an “idea” into a production capable part involves making many 
batches of test samples. Think in the thousands of batches and hundreds
of parts in each batch. You have a “search” process at the blank chopping
level. You also have a search at the resonator fabrication level. Getting the 
chopping part right is only a small part of the whole process….

One example:

I may have a wonderful “Bob Cut” that does a fine job over temperature. 
If a 5 Mhz 3rd overtone “Bob Cut”has a Q of 100,000 it isn’t going to show
up in a lot of OCXO’s …..The temperature stuff relates to the blank chopping
part. The Q gets into the details of the resonator design. 

Typically this design stuff gets done by folks who have PhD’s in this or that 
sub-type of crystal design. Even with that PhD, you still do these “mass search’
sorts of designs.  A full answer on most things crystal might take a couple 
books worth of detail …..

Bob

> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.