Using non-overtone crystal in overtone mode?

[Tim Shoppa]

Are "overtone" crystals cut differently than "fundamental" crystals?
Or are they just specified differently?

In particular, say I took a garden-variety 20MHz fundamental
microprocessor crystal and instead used it at its fifth overtone,
trying to hit 100 MHz. The LC network is there to make sure that it's
on its fifth overtone. Will this "misuse" mean that the oscillator
will be harder to start up, less stable, more noisy, ???, than a
crystal oscillator made out of a real overtone crystal? I don't mind
if I "miss" 100 MHz by a several tens or hundreds of ppm, as long as
it's stable there.

If anyone knows of a place that ships off-the-shelf 100 MHz fifth or
seventh overtone crystals, I can avoid this whole exercise....

Tim.

 

[RST Engineering (jw)]

I don't know why off-the-shelf crystals are needed when Jan Crystal (Ft.
Myers FL) will make the crystal to your specifications in a few days for the
same amount of money. They can do fifth ot at 100 MHz. quite easily.

Jim

If anyone knows of a place that ships off-the-shelf 100 MHz fifth or
seventh overtone crystals, I can avoid this whole exercise....

Tim.

 

[John Fields]

On Mon, 28 Feb 2005 13:27:04 -0800, Tim Wescott
<tim@wescottnospamdesign.com> wrote:

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.

Perhaps you're thinking of SAW devices?

---
No, I was thinking they vibrated in thickness compression. Thanks for
the correction.

--
John Fields

 

[Tim Wescott]

Larry Brasfield wrote:

"Tim Wescott" <tim@wescottnospamdesign.com> wrote
in message news:112734jd5n2lf2f@corp.supernews.com...
...

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.


One effect to watch out for with use of unspecified
overtone modes is that the behavior of the resonator
is not ideal; the presence or size of nearby spurs and
the Q depend on how uniform the thickness is that
determines frequency and the placement and size of
contact metal. The wavelength is typically much less
than the dimension along the non-shearing axis, so
having a single mode of resonance near the nominal
frequency or its overtones is not guaranteed, except
by careful construction and verification. So, clearly,
a guarantee about the behavior near the fundamental
resonance cannot be extended to the overtone modes.

If I was trying to build a stable and pure oscillator
operating at a crystal overtone, I would buy the
crystal specified for the overtone I would be using.

I pointed that out in a previous post. But hey -- wouldn't it be fun to

have an oscillator that yodels?

--

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

 

[J M Noeding]

On Mon, 28 Feb 2005 13:29:15 -0800, "RST Engineering \(jw\)"
<jim@rstengineering.com> wrote:

I don't know why off-the-shelf crystals are needed when Jan Crystal (Ft.
Myers FL) will make the crystal to your specifications in a few days for the
same amount of money. They can do fifth ot at 100 MHz. quite easily.

Jim



If anyone knows of a place that ships off-the-shelf 100 MHz fifth or
seventh overtone crystals, I can avoid this whole exercise....

Tim.


a CB xtal will probably operate on 100MHz, althouth I've only seen

applications for 45 and 81MHz

-jm

---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm

 

[Active8]

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.

Dialog news reader's tip popped up to say that CE is "creative
editing". It doesn't KWTF IDNKWTFIAS is, but I got everything but
the IAS part.

--
Best Regards,
Mike

 

[Active8]

On Mon, 28 Feb 2005 13:29:15 -0800, RST Engineering (jw) wrote:

I don't know why off-the-shelf crystals are needed when Jan Crystal (Ft.
Myers FL) will make the crystal to your specifications in a few days for the
same amount of money. They can do fifth ot at 100 MHz. quite easily.

Jim

Jan's what I was about to suggest. I thought the rock I needed would

have been off the shelf, but they made it and sent the test results.
--
Best Regards,
Mike

 

[Tim Wescott]

Active8 wrote:

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.


Dialog news reader's tip popped up to say that CE is "creative
editing". It doesn't KWTF IDNKWTFIAS is, but I got everything but
the IAS part.

IDNKWTFIAS: I Don't Know What I Am Saying.

--

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

 

[Joerg]

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

 

[Rich Grise]

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

 

[Tim Wescott]

Rich Grise wrote:

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

 

[RST Engineering]

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.

 

[Joerg]

Hello Jim,

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

 

[Terry Given]

Rich Grise wrote:

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

 

[Terry Given]

RST Engineering wrote:

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

 

[Michael A. Terrell]

Terry Given wrote:

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

 

[John Woodgate]

I read in sci.electronics.design that Terry Given <my_name@ieee.org>
wrote (in <ndSUd.5424$1S4.590975@news.xtra.co.nz&gt about 'Using non-
overtone crystal in overtone mode?', on Tue, 1 Mar 2005:

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

 

[John Woodgate]

I read in sci.electronics.design that douglas dwyer
<dd@ddwyer.demon.co.uk> wrote (in <bdN6PZDlM6ICFwQ2@ddwyer.demon.co.uk&gt
about 'Using non-overtone crystal in overtone mode?', on Mon, 28 Feb
2005:

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

 

[Paul Burke]

John Woodgate wrote:

OK, silly I know, but I cant figure out YMMV...
Year 2005. (;-)

Honestly John! That should be AMMV.

 

[John Woodgate]

I read in sci.electronics.design that Paul Burke <paul@scazon.com> wrote
(in <38j07rF5o6pl4U1@individual.net&gt about 'Using non-overtone crystal
in overtone mode?', on Tue, 1 Mar 2005:

John Woodgate wrote:
OK, silly I know, but I cant figure out YMMV...
Year 2005. (;-)

Honestly John! That should be AMMV.

The promulgation of a 'horrible hybrid' is justified in pursuit of a
whimsical coincidence.
--
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