[time-nuts] Are there SC-crystals out there in the wild that are not Overtone?

[Attila Kinali]

Hoi Gerhard!

On Wed, 26 Feb 2020 01:42:11 +0100
Gerhard Hoffmann via time-nuts <time-nuts at lists.febo.com> wrote:

> Pics are there:
> 
> < 
> https://www.flickr.com/photos/137684711@N07/49585174873/in/album-72157662535945536/ 
>     >

Nice pictures! Thanks!

Do you know what the two coils/transformers that were glued to the
outside of the inner oven were for?

 
> But I could not see anything at 1 or 1.6666 MHz, so it should be a 
> fundamental crystal?

Judging from the specs, very unlikely. The short-term and long-term
stability are consistent with what I expect of an 3rd overtone 5MHz
SC cut crystal. The lower Q of a fundamental mode crystal would result
in a higher close in phase noise and the thinner plate would lead to
a higher aging rate at tau of one day. I can see two reasons for you
to not see the fundamental mode: Either your measurement setup was not
done properly to measure quartz crystals (see Bob's comment on impedance)
or they manufactured the crystal for low fundamental mode.

Bernd Neubig has written a few documents on how to measure crystals
properly, which should be available from Axtal's website, if I'm not
mistaken.

			Attila Kinali

-- 
In science if you know what you are doing you should not be doing it.
In engineering if you do not know what you are doing you should not be doing it.
        -- Richard W. Hamming, The Art of Doing Science and Engineering