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.

Tim Shoppa wrote:

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.

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.

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.

--

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

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 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

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

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

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 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

I read in sci.electronics.design that Terry Given
wrote (in ) 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 wrote:
OK, silly I know, but I cant figure out YMMV...
Year 2005. (;-)

Honestly John! That should be AMMV.