Using non-overtone crystal in overtone mode?
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Using non-overtone crystal in overtone mode?
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Joerg
Guest
Posted: Tue Mar 01, 2005 6:10 am    Post subject: Re: Using non-overtone crystal in overtone mode? Reply with quote
Hello Tim,

As Douglas said the frequency may be a bit off unless you get a crystal
made for 5th. An alternative for the 20MHz garden variety would be to
make a 20MHz oscillator, run it into a fast gate and fish out the 5th
the old fashioned way, with an LC circuit. Then run that through a gate
again if needed.

Regards, Joerg

http://www.analogconsultants.com

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Rich Grise
Guest
Posted: Tue Mar 01, 2005 6:10 am    Post subject: Re: Using non-overtone crystal in overtone mode? Reply with quote
On Mon, 28 Feb 2005 12:07:49 -0800, Tim Wescott wrote:
Quote:

IIRC Digi-Key has 100MHz crystals, but I may be remembering 100MHz
oscillators. YMMV. IDNKWTFIAS. Caviat Emptor (so _that's_ what CE
----------
means! Here I thought it was a quality mark). Etc.

I Do Not Know WTF I Am Saying?

Thanks,
Rich
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Tim Wescott
Guest
Posted: Tue Mar 01, 2005 6:10 am    Post subject: Re: Using non-overtone crystal in overtone mode? Reply with quote
Rich Grise wrote:

Quote:
On Mon, 28 Feb 2005 12:07:49 -0800, Tim Wescott wrote:

IIRC Digi-Key has 100MHz crystals, but I may be remembering 100MHz
oscillators. YMMV. IDNKWTFIAS. Caviat Emptor (so _that's_ what CE

----------

means! Here I thought it was a quality mark). Etc.


I Do Not Know WTF I Am Saying?

Now Rich, that's being awfully harsh on yourself.


--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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RST Engineering
Guest
Posted: Tue Mar 01, 2005 6:10 am    Post subject: Re: Using non-overtone crystal in overtone mode? Reply with quote
That is total and absolute bullpuckey.

Jim


Quote:
---
You can use a fundamental mode crystal as an overtone oscillator, but
even if you can get it to oscillate, it won't be generating an
overtone at 100MHz, since overtone modes of oscillation aren't
harmonically related to the fundamental.
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Michael A. Terrell
Guest
Posted: Tue Mar 01, 2005 6:10 am    Post subject: Re: Using non-overtone crystal in overtone mode? Reply with quote
Terry Given wrote:
Quote:

OK, silly I know, but I cant figure out YMMV...

Your Mileage May Vary


--
Beware of those who post from srvinet.com!

Michael A. Terrell
Central Florida
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Terry Given
Guest
Posted: Tue Mar 01, 2005 6:10 am    Post subject: Re: Using non-overtone crystal in overtone mode? Reply with quote
RST Engineering wrote:
Quote:
That is total and absolute bullpuckey.

Jim



---
You can use a fundamental mode crystal as an overtone oscillator, but
even if you can get it to oscillate, it won't be generating an
overtone at 100MHz, since overtone modes of oscillation aren't
harmonically related to the fundamental.

sorry dude, 50 years of IEEE UFFC papers suggest *you* are wrong. I was
surprised when I learned this too.

Cheers
Terry
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Terry Given
Guest
Posted: Tue Mar 01, 2005 6:10 am    Post subject: Re: Using non-overtone crystal in overtone mode? Reply with quote
Rich Grise wrote:
Quote:
On Mon, 28 Feb 2005 12:07:49 -0800, Tim Wescott wrote:

IIRC Digi-Key has 100MHz crystals, but I may be remembering 100MHz
oscillators. YMMV. IDNKWTFIAS. Caviat Emptor (so _that's_ what CE

----------

means! Here I thought it was a quality mark). Etc.


I Do Not Know WTF I Am Saying?

Thanks,
Rich


OK, silly I know, but I cant figure out YMMV...

OTOH, WTF, IAAR

Cheers
Terry
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Joerg
Guest
Posted: Tue Mar 01, 2005 6:10 am    Post subject: Re: Using non-overtone crystal in overtone mode? Reply with quote
Hello Jim,

Quote:
That is total and absolute bullpuckey.



Huh? See the 2nd paragraph (mode):

http://www.euroquartz.co.uk/tech-xtal.htm

Regards, Joerg

http://www.analogconsultants.com
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Ken Smith
Guest
Posted: Tue Mar 01, 2005 3:04 pm    Post subject: Re: Using non-overtone crystal in overtone mode? Reply with quote
In article <1126ufulsdj5s93@corp.supernews.com>,
Tim Wescott <tim@wescottnospamdesign.com> wrote:
[....]
Quote:
Overtone crystal cuts are not fundamentally different from fundamental
crystal cuts, so to a 1st-order approximation they'll work. Crystals do
have spurious responses that can cause mode jumping, and these responses
don't necessarily map the same way the overtones do, so using a 20MHz
crystal at 100MHz may or may not work, depending on the luck of the
draw. Other than that I don't know of any differences.


There is a whole science of crystals all on its own. When they make a
crystal they make a thin disk of material. You would normally expect the
edge of the disk to simply be at right angles. Instead it looks like
this:



***********************
*
*
*
*
*************************

The exact angle and depth of that chamfer is how they control which
overtones are selected for and which are supressed. In fundamental
crystals, the maker usually grinds the chamfer so as to reduce the 3rd
harmonic responce.


--
--
kensmith@rahul.net forging knowledge
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Ken Smith
Guest
Posted: Tue Mar 01, 2005 3:07 pm    Post subject: Re: Using non-overtone crystal in overtone mode? Reply with quote
In article <11276jobn8vot2f@corp.supernews.com>,
Tim Wescott <tim@wescottnospamdesign.com> wrote:
[....]
Quote:
I pointed that out in a previous post. But hey -- wouldn't it be fun to
have an oscillator that yodels?

No, it isn't fun. Trust me :<

--
--
kensmith@rahul.net forging knowledge
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Ken Smith
Guest
Posted: Tue Mar 01, 2005 3:21 pm    Post subject: Re: Using non-overtone crystal in overtone mode? Reply with quote
In article <omu621p01vkm51l99jrvtold0pcgkt09rh@4ax.com>,
John Fields <jfields@austininstruments.com> wrote:
[..]
Quote:
You can use a fundamental mode crystal as an overtone oscillator, but
even if you can get it to oscillate, it won't be generating an
overtone at 100MHz, since overtone modes of oscillation aren't
harmonically related to the fundamental. It's more like the slab of
crystal is vibrating like the drumhead of a steel drum with small
areas of the slab vibrating at higher frequencies, instead of the
entire slab virbarting at just one frequency.

No, its more like a jello when you jiggle the dish side to side. The main
action of an AT cut is shear mode. In the harmonics, the motion looks
kind of like this:


Quote:







If you think about the top two lines of text in my little drawing. I
think it is obvious that if the maker thinned it down by one line of text
just as you come to the edge, that portion of the crystal would not work
well at this harmonic. This is what they do in crystals intended for
fundamental operation. It knocks that activity down by several dB at the
overtone. This makes it very unlikely that a simple oscillator will take
off at an overtone.
--
--
kensmith@rahul.net forging knowledge
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John Woodgate
Guest
Posted: Tue Mar 01, 2005 3:33 pm    Post subject: Re: Using non-overtone crystal in overtone mode? Reply with quote
I read in sci.electronics.design that Terry Given <my_name@ieee.org>
wrote (in <ndSUd.5424$1S4.590975@news.xtra.co.nz>) about 'Using non-
overtone crystal in overtone mode?', on Tue, 1 Mar 2005:

Quote:
OK, silly I know, but I cant figure out YMMV...

Year 2005. (;-)
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
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Ken Smith
Guest
Posted: Tue Mar 01, 2005 3:34 pm    Post subject: Re: Using non-overtone crystal in overtone mode? Reply with quote
In article <112734jd5n2lf2f@corp.supernews.com>,
Tim Wescott <tim@wescottnospamdesign.com> wrote:
[...]
Quote:
In an AT cut crystal the overtone modes are close, but not exactly on,
the odd harmonics of the fundamental. Furthermore, all of the
literature that I've read on AT cut crystals reports that they vibrate
in the bulk of the crystal, in shear mode -- see figure 7 here:
http://literature.agilent.com/litweb/pdf/5965-7662E.pdf.

Yes

In the ideal AT cut crystal "c mode" shear is the only activity. In the SC
cut, the "b" and "a" modes appear. The extra complexity of the mode
selection circuit is part of the reason that SC based OCXOs cost so much.

--
--
kensmith@rahul.net forging knowledge
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John Woodgate
Guest
Posted: Tue Mar 01, 2005 3:36 pm    Post subject: Re: Using non-overtone crystal in overtone mode? Reply with quote
I read in sci.electronics.design that douglas dwyer
<dd@ddwyer.demon.co.uk> wrote (in <bdN6PZDlM6ICFwQ2@ddwyer.demon.co.uk>)
about 'Using non-overtone crystal in overtone mode?', on Mon, 28 Feb
2005:
Quote:
Overtone crystals are mechanical resonators and the overtone shear mode
which has additional shear planes within the volume wont occupy exactly
the same volume as the fundamental so the frequency will not be exactly
3X or 5X the fundamental but approx 2000ppm high or low?

I remember being told by a crystal 'expert' that with some cuts the
difference can be much larger than that. Is that so?
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
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Paul Burke
Guest
Posted: Tue Mar 01, 2005 4:50 pm    Post subject: Re: Using non-overtone crystal in overtone mode? Reply with quote
John Woodgate wrote:
Quote:
OK, silly I know, but I cant figure out YMMV...
Year 2005. (;-)

Honestly John! That should be AMMV.
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